Independent Bank (IBTX) 10-Q 29 Apr 21 2021 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2021	Apr. 27, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-35854
Entity Registrant Name	Independent Bank Group, Inc.
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	13-4219346
Entity Address, Address Line One	7777 Henneman Way
Entity Address, City or Town	McKinney,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75070-1711
City Area Code	972
Local Phone Number	562-9004
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	IBTX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		43,192,579
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001564618
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets
Cash and due from banks	$ 248,231	$ 250,485
Interest-bearing deposits in other banks	2,168,639	1,563,502
Cash and cash equivalents	2,416,870	1,813,987
Certificates of deposit held in other banks	4,482	4,482
Securities available for sale, at fair value	1,307,957	1,153,693
Loans held for sale (includes $53,930 and $71,769 carried at fair value, respectively)	57,799	82,647
Loans, net of allowance for credit losses of $165,827 and $87,820, respectively	12,604,930	12,978,238
Premises and equipment, net	250,002	249,467
Other real estate owned	475	475
Federal Home Loan Bank (FHLB) of Dallas stock and other restricted stock	20,338	20,305
Bank-owned life insurance (BOLI)	221,700	220,428
Deferred tax asset	18,804	3,933
Goodwill	994,021	994,021
Other intangible assets, net	84,925	88,070
Other assets	133,033	143,730
Total assets	18,115,336	17,753,476
Deposits:
Noninterest-bearing	4,466,310	4,164,800
Interest-bearing	10,337,482	10,234,127
Total deposits	14,803,792	14,398,927
FHLB advances	375,000	375,000
Other borrowings	308,350	312,175
Junior subordinated debentures	54,072	54,023
Other liabilities	81,005	97,980
Total liabilities	15,622,219	15,238,105
Commitments and contingencies	0	0
Stockholders’ equity:
Preferred stock (0 and 0 shares outstanding, respectively)	0	0
Common stock (43,193,257 and 43,137,104 shares outstanding, respectively)	432	431
Additional paid-in capital	1,938,012	1,934,807
Retained earnings	535,375	543,800
Accumulated other comprehensive income	19,298	36,333
Total stockholders’ equity	2,493,117	2,515,371
Total liabilities and stockholders’ equity	$ 18,115,336	$ 17,753,476

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Loans held for sale, fair value option	$ 53,930	$ 71,769
Allowance for credit losses	$ (165,827)	$ (87,820)
Preferred stock, shares outstanding (shares)	0	0
Common stock, shares outstanding (shares)	43,193,257	43,137,104

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest income:
Interest and fees on loans	$ 140,152	$ 147,105
Interest on taxable securities	4,757	5,164
Interest on nontaxable securities	2,069	2,065
Interest on interest-bearing deposits and other	793	2,071
Total interest income	147,771	156,405
Interest expense:
Interest on deposits	13,007	28,071
Interest on FHLB advances	533	1,626
Interest on other borrowings	4,060	2,795
Interest on junior subordinated debentures	442	672
Total interest expense	18,042	33,164
Net interest income	129,729	123,241
Provision for credit losses	(2,500)	8,381
Net interest income after provision for credit losses	132,229	114,860
Noninterest income:
Service charges on deposit accounts	2,261	2,752
Investment management fees	2,043	1,986
Mortgage banking revenue	7,495	2,525
Loss on sale of loans	0	(42)
Gain on sale of other real estate	0	25
Gain on sale of securities available for sale	0	356
Loss on sale and disposal of premises and equipment	(7)	(63)
Increase in cash surrender value of BOLI	1,272	1,341
Other	5,545	5,692
Total noninterest income	18,609	14,572
Noninterest expense:
Salaries and employee benefits	43,659	38,660
Occupancy	9,606	10,037
Communications and technology	5,536	5,552
FDIC assessment	1,705	1,752
Advertising and public relations	238	611
Other real estate owned expenses, net	8	374
Amortization of other intangible assets	3,145	3,176
Professional fees	3,670	4,214
Acquisition expense, including legal	0	549
Other	7,546	9,504
Total noninterest expense	75,113	74,429
Income before taxes	75,725	55,003
Income tax expense	15,745	10,836
Net income	$ 59,980	$ 44,167
Basic earnings per share (usd per share)	$ 1.39	$ 1.03
Diluted earnings per share (usd per share)	$ 1.39	$ 1.03

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 59,980	$ 44,167
Other comprehensive (loss) income before tax:
Change in net unrealized (losses) gains on available for sale securities during the year	(21,563)	14,976
Reclassification for amount realized through sales of securities available for sale included in net income	0	(356)
Other comprehensive (loss) income before tax	(21,563)	14,620
Income tax (benefit) expense	(4,528)	3,258
Other comprehensive (loss) income, net of tax	(17,035)	11,362
Comprehensive income	$ 42,945	$ 55,529

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock $0.01 Par Value	Common Stock $0.01 Par Value	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Cumulative effect of change in accounting principles	Cumulative effect of change in accounting principlesRetained Earnings	Adjusted beginning balance	Adjusted beginning balanceCommon Stock $0.01 Par Value	Adjusted beginning balanceAdditional Paid in Capital	Adjusted beginning balanceRetained Earnings	Adjusted beginning balanceAccumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2019	$ 2,339,773	$ 0	$ 430	$ 1,926,359	$ 393,674	$ 19,310
Beginning balance (shares) at Dec. 31, 2019			42,950,228
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,167				44,167
Other comprehensive income net of tax	11,362					11,362
Common stock repurchased (shares)			(2,629)
Common stock repurchased	(145)		$ 0		(145)
Restricted stock granted (shares)			94,177
Restricted stock granted	0
Stock based compensation expense	1,882			1,882
Cash dividends ($0.30 and $0.25 per share for the three months ended March 31, 2021 and 2020, respectively)	(10,754)				(10,754)
Ending balance at Mar. 31, 2020	2,386,285	0	$ 430	1,928,241	426,942	30,672
Ending balance (shares) at Mar. 31, 2020			43,041,776
Beginning balance at Dec. 31, 2020	2,515,371	0	$ 431	1,934,807	543,800	36,333	$ (53,880)	$ (53,880)	$ 2,461,491	$ 431	$ 1,934,807	$ 489,920	$ 36,333
Beginning balance (shares) at Dec. 31, 2020			43,137,104							43,137,104
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	59,980				59,980
Other comprehensive income net of tax	(17,035)					(17,035)
Common stock repurchased (shares)			(22,835)
Common stock repurchased	(1,489)		$ 0		(1,489)
Restricted stock forfeited (shares)			(4,506)
Restricted stock forfeited	0		$ 0
Restricted stock granted (shares)			83,494
Restricted stock granted	0		$ 1	(1)
Stock based compensation expense	3,206			3,206
Cash dividends ($0.30 and $0.25 per share for the three months ended March 31, 2021 and 2020, respectively)	(13,036)				(13,036)
Ending balance at Mar. 31, 2021	$ 2,493,117	$ 0	$ 432	$ 1,938,012	$ 535,375	$ 19,298
Ending balance (shares) at Mar. 31, 2021			43,193,257

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Statement of Stockholders' Equity [Abstract]
Preferred stock par value (usd per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Preferred stock shares authorized (shares)	10,000,000	10,000,000	10,000,000	10,000,000
Common stock par value (usd per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock shares authorized (shares)	100,000,000	100,000,000	100,000,000	100,000,000
Dividends paid (usd per share)	$ 0.30	$ 0.25
Restricted stock granted	$ 0	$ 0
Cumulative effect reduction to retained earnings	$ 2,493,117	$ 2,386,285	$ 2,515,371	$ 2,339,773

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 59,980	$ 44,167
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation expense	3,160	3,154
Accretion income recognized on acquired loans	(6,245)	(9,142)
Amortization of other intangibles assets	3,145	3,176
Amortization of premium on securities, net	982	619
Amortization of discount and origination costs on borrowings	224	159
Stock based compensation expense	3,206	1,882
Excess tax (benefit) expense on restricted stock vested	(194)	80
FHLB stock dividends	(33)	(168)
Gain on sale of securities available for sale	0	(356)
Loss on sale and disposal of premises and equipment	7	63
Loss on sale of loans	0	42
Gain on sale of other real estate owned	0	(25)
Impairment of other assets	9	0
Provision for credit losses	(2,500)	8,381
Deferred tax expense	4,771	2,471
Increase in cash surrender value of BOLI	(1,272)	(1,341)
Net gain on mortgage loans held for sale	(5,299)	(3,916)
Originations of loans held for sale	(217,882)	(107,580)
Proceeds from sale of loans held for sale	248,029	107,714
Net change in other assets	10,833	(10,935)
Net change in other liabilities	(23,033)	1,980
Net cash provided by operating activities	77,888	40,425
Cash flows from investing activities:
Proceeds from maturities, calls and pay downs of securities available for sale	7,200,419	1,528,836
Proceeds from sale of securities available for sale	0	13,100
Purchases of securities available for sale	(7,372,228)	(1,530,779)
Purchases of FHLB stock and other restricted stock	0	(25,211)
Proceeds from redemptions of FHLB stock and other restricted stock	0	106
Proceeds from sale of loans	0	1,455
Net loans originated held for investment	(33,926)	(89,252)
Originations of mortgage warehouse purchase loans	(8,419,896)	(4,523,819)
Proceeds from pay-offs of mortgage warehouse purchase loans	8,767,994	4,414,527
Additions to premises and equipment	(3,811)	(5,948)
Proceeds from sale of premises and equipment	21	66
Proceeds from sale of other real estate owned	0	4,200
Net cash provided by (used in) investing activities	138,573	(212,719)
Cash flows from financing activities:
Net increase (decrease) in demand deposits, money market and savings accounts	456,447	(9,596)
Net decrease in time deposits	(51,582)	(48,974)
Proceeds from FHLB advances	0	1,100,000
Repayments of FHLB advances	0	(450,000)
Proceeds from other borrowings	2,500	0
Repayments of other borrowings	(6,500)	(24,500)
Repurchase of common stock	(1,489)	(145)
Dividends paid	(12,954)	(10,754)
Net cash provided by financing activities	386,422	556,031
Net change in cash and cash equivalents	602,883	383,737
Cash and cash equivalents at beginning of period	1,813,987	565,170
Cash and cash equivalents at end of period	$ 2,416,870	$ 948,907

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Nature of operations: Independent Bank Group, Inc. (IBG) through its subsidiary, Independent Bank, a Texas state banking corporation, doing business as Independent Financial, (Bank) (collectively known as the Company), provides a full range of banking services to individual and corporate customers in the North, Central and Southeast, Texas areas and along the Colorado Front Range, through its various branch locations in those areas. The Company is engaged in traditional community banking activities, which include commercial and retail lending, deposit gathering, investment and liquidity management activities. The Company’s primary deposit products are demand deposits, money market accounts and certificates of deposit and its primary lending products are commercial business and real estate, real estate mortgage and consumer loans. Basis of presentation: The accompanying consolidated financial statements include the accounts of IBG and all other entities in which IBG has controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. In addition, the Company wholly-owns nine statutory business trusts that were formed for the purpose of issuing trust preferred securities and do not meet the criteria for consolidation. The consolidated interim financial statements are unaudited, but include all adjustments, which, in the opinion of management, are necessary for a fair presentation of the results of the periods presented. All such adjustments were of a normal and recurring nature. These financial statements should be read in conjunction with the financial statements and the notes thereto in the Company's Annual Report on Form 10-K for the year ended December 31, 2020. The consolidated balance sheet at December 31, 2020 has been derived from the audited financial statements as of that date, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. Accounting standards codification: The Financial Accounting Standards Board's (FASB) Accounting Standards Codification (ASC) is the officially recognized source of authoritative U.S. generally accepted accounting principles (GAAP) applicable to all public and non-public non-governmental entities. Rules and interpretive releases of the SEC under the authority of federal securities laws are also sources of authoritative GAAP for SEC registrants. All other accounting literature is considered non-authoritative. Citing particular content in the ASC involves specifying the unique numeric path to the content through the Topic, Subtopic, Section and Paragraph structure. Segment reporting: The Company has one reportable segment. The Company’s chief operating decision-maker uses consolidated results to make operating and strategic decisions. Reclassifications: Certain prior period financial statement and disclosure amounts have been reclassified to conform to current period presentation. The reclassifications have no effect on net income or stockholders' equity as previously reported. Use of estimates: The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Accordingly, actual results could differ from those estimates. The material estimates included in the financial statements relate to the allowance for credit losses, the valuation of goodwill and valuation of assets and liabilities acquired in business combinations. Accounting changes: On January 1, 2020, ASU 2016-13, Financial Instruments - Credit Losses (Topic 326) (ASC 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13) , as amended, became effective for the Company. ASU 2016-13 replaces the incurred loss methodology with an expected loss methodology that is referred to as the current expected credit loss (CECL) methodology. The measurement of expected credit losses under the CECL methodology is applicable to financial assets measured at amortized cost, including loan receivables and held-to-maturity debt securities. It also applies to off-balance-sheet credit exposures not accounted for as insurance (loan commitments, standby letters of credit, financial guarantees, and other similar instruments). The CECL model requires the measurement of all expected credit losses on applicable financial assets based on historical experience, current conditions, and reasonable and supportable forecasts. In addition, ASU 2016-13 includes certain changes to the accounting for available-for-sale securities such as requiring credit-related impairments to be recognized as an allowance for credit losses rather than as a direct write-down of the securities amortized cost basis when management does not intend to sell or believes that it is more likely than not they will be required to sell securities prior to recovery of the securities amortized cost basis. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) was signed by the President of the United States that included an option for financial institutions to delay the implementation of ASU 2016-13 until the earlier of the termination date of the national emergency declaration by the President or December 31, 2020. On December 27, 2020, the Consolidated Appropriations Act, 2021 (Act 2021), was signed into law which further extended the implementation date of CECL to the earlier of the first day of the entity’s fiscal year that begins after the date on which the COVID-19 national emergency terminates or January 1, 2022. Under this option, the Company elected to delay implementation of ASU 2016-13 and calculated and recorded its provision for loan losses under the incurred loss model that existed prior to ASU 2016-13 for the year ended December 31, 2020. With regard to Act 2021 amendments, the SEC staff indicated it would not object to a registrant early adopting on December 31, 2020, retrospective to January 1, 2020, or January 1, 2021, effective as of January 1, 2021. Under this guidance, the Company elected to adopt ASU 2016-13 with an effective implementation date of January 1, 2021. The Company adopted ASU 2016-13 using the modified retrospective method for all financial assets measured at amortized cost and off-balance sheet credit exposures. As a result of this adoption, the Company recognized a cumulative effect reduction to retained earnings totaling $53,880, net of a recorded deferred tax asset of $15,113, and reclassed $13,035 of allowance for credit loss related to financial assets purchased with credit deterioration (PCD) that were previously classified as purchased credit impaired (PCI) and accounted for under ASC 310-30 as discussed below. Results for periods beginning after January 1, 2021 are presented in accordance with ASU 2016-13 while prior period amounts continue to be reported in accordance with previously applicable GAAP. The Company adopted ASU 2016-13 using the prospective transition approach for PCD assets. In accordance with the standard, management did not reassess whether PCI assets met the criteria of PCD assets as of the date of adoption. On January 1, 2021, the amortized cost basis of the PCD assets were adjusted to reflect the addition of the allowance for credit losses. The remaining noncredit discount (based on the adjusted amortized cost basis) will be accreted into interest income at the effective interest rate as of January 1, 2021. The following table illustrates the impact of ASU 2016-13 on the allowances for credit losses as of January 1, 2021, the date of adoption: January 1, 2021 Pre-Adoption Allowance Impact of Adoption Post-Adoption Allowance Assets: Allowance for credit losses on Loans: Commercial $ 27,311 $ 17,103 $ 44,414 Commercial real estate, construction, land and land development 50,123 59,683 109,806 Residential real estate 6,786 (2,115) 4,671 Single-family interim construction 2,156 7,179 9,335 Agricultural 337 (178) 159 Consumer 442 (110) 332 Other 242 (224) 18 Unallocated 423 (423) — $ 87,820 $ 80,915 $ 168,735 Liabilities: Allowance for credit losses on off-balance-sheet credit exposures $ — $ 1,113 $ 1,113 In connection with the adoption of ASC 326, the Company revised certain accounting policies and implemented certain accounting policy elections. The revised accounting policies are described below. Securities: Securities classified as available for sale are those debt securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity. Any decision to sell a security classified as available for sale would be based on various factors, including significant movements in interest rates, changes in the maturity mix of the Company's assets and liabilities, liquidity needs, regulatory capital considerations and other similar factors. Securities available for sale are reported at fair value with unrealized gains or losses reported as a separate component of other comprehensive income, net of tax. The amortization of premiums and accretion of discounts, computed by the interest method generally over their contractual lives, are recognized in interest income. Premiums on callable securities are amortized to their earliest call date. Realized gains or losses, determined on the basis of the cost of specific securities sold, are included in earnings on the trade date. Allowance for credit losses - available-for-sale securities: For available-for-sale securities in an unrealized loss position, the Company first assesses whether it intends to sell or it is more-likely-than-not that we will be required to sell the securities before recovery of the amortized cost basis. If either of these criteria is met, the securities amortized cost basis is written down to fair value as a current period expense. If either of the above criteria is not met, the Company evaluates whether the decline in fair value is the result of credit losses or other factors. In making this assessment, management may consider various factors including the extent to which fair value is less than amortized cost, performance of any underlying collateral and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected are compared to the amortized cost basis of the security and any excess of the amortized cost basis over the present value of expected cash flows is recorded as an allowance for credit loss, limited to the amount by which the fair value is less than the amortized cost basis. Any impairment not recorded through an allowance for credit loss is recognized in other comprehensive income as a non credit-related impairment. Management has made a policy election to exclude accrued interest receivable on available-for-sale securities from the estimate of credit losses and report accrued interest separately in other assets in the consolidated balance sheets. Changes in the allowance for credit losses are recorded as provision for (or reversal of) credit losses. Available-for-sale securities are charged-off against the allowance or, in the absence of any allowance, written down through income when deemed uncollectible by management or when either of the aforementioned criteria regarding intent or requirement to sell is met. Acquired loans: Loans acquired in connection with a business combination are recorded at their acquisition-date fair value. The allowance for credit losses related to the acquired loan portfolio is not carried over. Acquired loans are classified into two categories based on the credit risk characteristics of the underlying borrowers as either purchased credit deteriorated (PCD) loans, or loans with no evidence of credit deterioration (non-PCD). PCD loans are defined as a loan or pool of loans that have experienced more-than-insignificant credit deterioration since the origination date. For PCD loans, an initial allowance is established on the acquisition date using the same methodology as other loans held for investment and combined with the fair value of the loan to arrive at acquisition date amortized cost. Accordingly, no provision for credit losses is recognized on PCD loans at the acquisition date. Subsequent to the acquisition date, changes to the allowance are recognized in the provision for credit losses. Non-PCD loans are pooled into segments together with originated held for investment loans that share similar risk characteristics and have an allowance established on the acquisition date, which is recognized in the current period provision for credit losses. Determining the fair value of the acquired loans involves estimating the principal and interest payment cash flows expected to be collected on the loans and discounting those cash flows at a market rate of interest. For PCD loans, the non-credit discount or premium is allocated to individual loans as determined by the difference between the loan’s unpaid principal balance and amortized cost basis. The non-credit premium or discount is recognized into interest income on a level yield basis over the remaining expected life of the loan. For non-PCD loans, the fair value discount or premium is allocated to individual loans and recognized into interest income on a level yield basis over the remaining expected life of the loan. Prior to January 1, 2021, loans acquired in a business combination that had evidence of credit impairment and for which it was probable, at acquisition, that the Company would be unable to collect all contractually required payments receivable were considered PCI. PCI loans were accounted for individually or aggregated into pools of loans based on common risk characteristics such as credit grade, loan type, and date of origination. Loans, net: Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal balance, net of unearned interest, purchase premiums and discounts, deferred loan fees or costs and an allowance for credit losses. Loan origination fees, net of direct origination costs, are deferred and recognized as an adjustment to the related loan yield using the effective interest method without anticipating prepayments. Further information regarding the Company's accounting policies related to past due loans, non-accrual loans, collateral dependent loans and troubled debt restructurings is presented in Note 4 - Loans , N et and Allowance for Credit Losses on Loans . Allowance for credit losses on loans: In accordance with ASC 326, the allowance for credit losses on loans is a valuation account that is deducted from the amortized cost basis of loans to present management's best estimate of the net amount expected to be collected on the loans. Loans are charged against the allowance for credit losses when management believes that collectability of the principal is unlikely. Subsequent recoveries, if any, are credited to the allowance. The allowance is increased by provisions reported in the income statement as a component of provision for credit losses. Management has made the accounting policy election to exclude accrued interest receivable on loans from the estimate of credit losses and reports accrued interest separately in other assets in the consolidated balance sheets. Further information regarding Company policies and methodology used to estimate the allowance for credit losses on loans is presented in Note 4 - Loans, Net and Allowance for Credit Losses on Loans . Allowance for credit losses on off-balance-sheet credit exposures: The allowance for credit losses on off-balance-sheet credit exposures is a liability account, calculated in accordance with ASC 326, representing expected credit losses over the contractual period for which the Company is exposed to credit risk resulting from a contractual obligation to extend credit. No allowance is recognized if we have the unconditional right to cancel the obligation. The allowance is reported as a component of other liabilities in the consolidated balance sheets. Adjustments to the allowance are reported in the income statement as a component of provision for credit losses. Further information regarding Company policies and methodology used to estimate the allowance for credit losses on off-balance-sheet credit exposures is presented in Note 5 - Off-Balance Sheet Arrangements, Commitments and Contingencies . Subsequent events: Companies are required to evaluate events and transactions that occur after the balance sheet date but before the date the financial statements are issued. They must recognize in the financial statements the effect of all events or transactions that provide additional evidence of conditions that existed at the balance sheet date, including the estimates inherent in the financial statement preparation process. Entities shall not recognize the impact of events or transactions that provide evidence about conditions that did not exist at the balance sheet date but arose after that date. The Company has evaluated subsequent events through the date of filing these financial statements with the Securities and Exchange Commission (SEC) and noted no subsequent events requiring financial statement recognition or disclosure, except as disclosed in Note 11. Earnings per share: Basic earnings per common share is calculated as net income available to common shareholders divided by the weighted average number of common shares outstanding during the period. The unvested share-based payment awards that contain rights to nonforfeitable dividends are considered participating securities for this calculation. Diluted earnings per common share include the dilutive effect of additional potential common shares issuable under participating nonvested restricted stock awards as well as performance stock units (PSUs). The participating nonvested common stock was not included in dilutive shares as it was anti-dilutive for the three months ended March 31, 2021. Proceeds from the assumed exercise of dilutive participating nonvested restricted stock awards and PSUs are assumed to be used to repurchase common stock at the average market price. The following table presents a reconciliation of net income available to common shareholders and the number of shares used in the calculation of basic and diluted earnings per common share. Three Months Ended March 31, 2021 2020 Basic earnings per share: Net income $ 59,980 $ 44,167 Less: Undistributed earnings allocated to participating securities 487 209 Dividends paid on participating securities 134 68 Net income available to common shareholders $ 59,359 $ 43,890 Weighted average basic shares outstanding 42,731,456 42,741,399 Basic earnings per share $ 1.39 $ 1.03 Diluted earnings per share: Net income available to common shareholders $ 59,359 $ 43,890 Total weighted average basic shares outstanding 42,731,456 42,741,399 Add dilutive performance stock units 44,321 — Add dilutive participating securities — 8,559 Total weighted average diluted shares outstanding 42,775,777 42,749,958 Diluted earnings per share $ 1.39 $ 1.03 Anti-dilutive participating securities 202,811 —

Statement of Cash Flows

Statement of Cash Flows	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Statement of Cash Flows	Statement of Cash Flows As allowed by the accounting standards, the Company has chosen to report, on a net basis, its cash receipts and cash payments for time deposits accepted and repayments of those deposits, and loans made to customers and principal collections on those loans. The Company uses the indirect method to present cash flows from operating activities. Other supplemental cash flow information is presented below: Three Months Ended March 31, 2021 2020 Cash transactions: Interest expense paid $ 21,785 $ 35,400 Income taxes paid $ 8 $ — Noncash transactions: Deferred dividend equivalents $ 82 $ — Transfers of loans to other real estate owned $ — $ 3,914 Loans to facilitate the sale of other real estate owned $ — $ 1,564 Securities purchased, not yet settled $ 5,000 $ — Right-of-use assets obtained in exchange for lease liabilities $ 57 $ — Transfer of premises and equipment to other assets $ 88 $ —

Securities Available for Sale

Securities Available for Sale	3 Months Ended
	Mar. 31, 2021
Debt Securities, Available-for-sale [Abstract]
Securities Available for Sale	Securities Available for Sale Securities available for sale have been classified in the consolidated balance sheets according to management’s intent. The amortized cost of securities and their approximate fair values at March 31, 2021 and December 31, 2020 are as follows: Amortized Cost (1) Gross Gross Fair Securities Available for Sale March 31, 2021 U.S. treasuries $ 33,051 $ 1,401 $ — $ 34,452 Government agency securities 295,580 2,806 (8,746) 289,640 Obligations of state and municipal subdivisions 373,045 16,044 (1,233) 387,856 Corporate bonds 28,494 580 (79) 28,995 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 552,910 17,777 (4,873) 565,814 Other securities 1,200 — — 1,200 $ 1,284,280 $ 38,608 $ (14,931) $ 1,307,957 December 31, 2020 U.S. treasuries $ 43,060 $ 1,648 $ — $ 44,708 Government agency securities 247,764 3,169 (1,916) 249,017 Obligations of state and municipal subdivisions 373,017 20,168 (20) 393,165 Corporate bonds 21,496 608 (2) 22,102 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 421,916 21,678 (93) 443,501 Other securities 1,200 — — 1,200 $ 1,108,453 $ 47,271 $ (2,031) $ 1,153,693 ____________ (1) Excludes accrued interest receivable of $5,206 and $6,242 at March 31, 2021 and December 31, 2020, respectively, that is recorded in other assets on the accompanying consolidated balance sheets. Securities with a carrying amount of approximately $779,138 and $738,519 at March 31, 2021 and December 31, 2020, respectively, were pledged primarily to secure deposits. Proceeds from sale of securities available for sale and gross gains and gross losses for the three months ended March 31, 2021 and 2020 were as follows: Three Months Ended March 31, 2021 2020 Proceeds from sale $ — $ 13,100 Gross gains $ — $ 359 Gross losses $ — $ 3 The amortized cost and estimated fair value of securities available for sale at March 31, 2021, by contractual maturity, are shown below. Maturities of mortgage-backed securities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. March 31, 2021 Securities Available for Sale Amortized Cost (1) Fair Value Due in one year or less $ 27,652 $ 27,986 Due from one year to five years 137,914 143,780 Due from five to ten years 247,804 249,486 Thereafter 318,000 320,891 731,370 742,143 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 552,910 565,814 $ 1,284,280 $ 1,307,957 ____________ (1) Excludes accrued interest receivable of $5,206 and $6,242 at March 31, 2021 and December 31, 2020, respectively, that is recorded in other assets on the accompanying consolidated balance sheets. The number of securities, unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of March 31, 2021 and December 31, 2020, are summarized as follows: Less Than 12 Months Greater Than 12 Months Total Description of Securities Number of Securities Estimated Unrealized Number of Securities Estimated Unrealized Estimated Unrealized Securities Available for Sale March 31, 2021 Government agency securities 31 $ 181,215 $ (8,746) — $ — $ — $ 181,215 $ (8,746) Obligations of state and municipal subdivisions 12 46,956 (1,233) — — — 46,956 (1,233) Corporate bonds 3 5,421 (79) — — — 5,421 (79) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 33 188,714 (4,873) — — — 188,714 (4,873) 79 $ 422,306 $ (14,931) — $ — $ — $ 422,306 $ (14,931) December 31, 2020 Government agency securities 20 112,897 (1,916) — — — 112,897 (1,916) Obligations of state and municipal subdivisions 2 3,786 (20) — — — 3,786 (20) Corporate bonds 1 998 (2) — — — 998 (2) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 10 41,344 (93) — — — 41,344 (93) 33 $ 159,025 $ (2,031) — $ — $ — $ 159,025 $ (2,031) At March 31, 2021 , management's review of all available for sale securities at an unrealized loss position determined that the losses resulted from factors not related to credit quality. This conclusion is based on management's analysis of the underlying risk characteristics, including credit ratings, and other qualitative factors for each security type in our portfolio. The unrealized losses are generally due to increases in market interest rates. Furthermore, the Company has the intent to hold these securities until maturity or a forecasted recovery, and it is more likely than not that the Company will not have to sell the securities before the recovery of their cost basis. As such, there is no allowance for credit losses on available for sale securities recognized as of March 31, 2021 .

Loans, Net and Allowance for Cr

Loans, Net and Allowance for Credit Losses on Loans	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Loans, Net and Allowance for Loan Losses	Loans, Net and Allowance for Credit Losses on Loans Loans, net, at March 31, 2021 and December 31, 2020, consisted of the following: March 31, December 31, 2021 2020 Commercial $ 3,596,654 $ 3,902,266 Real estate: Commercial 6,194,353 6,096,676 Commercial construction, land and land development 1,206,350 1,245,801 Residential 1,310,371 1,352,465 Single-family interim construction 312,975 326,575 Agricultural 74,820 85,014 Consumer 74,923 66,952 Other 311 346 Total loans (1)(2) 12,770,757 13,076,095 Deferred loan fees, net (1) — (10,037) Allowance for credit losses (165,827) (87,820) Total loans, net (2) $ 12,604,930 $ 12,978,238 ____________ (1) Loan class amounts are shown at amortized cost, net of deferred loan fees of $15,450 in accordance with ASC 326 at March 31, 2021 and shown at recorded investment at December 31, 2020. (2) Excludes accrued interest receivable of $54,683 and $54,328 at March 31, 2021 and December 31, 2020, respectively, that is recorded in other assets on the accompanying consolidated balance sheets. Loans with carrying amounts of $6,721,999 and $6,743,350 at March 31, 2021 and December 31, 2020, respectively, were pledged to secure Federal Home Loan Bank borrowing capacity and Federal Reserve Bank discount window borrowing capacity. The Company has certain lending policies and procedures in place that are designed to maximize loan income within an acceptable level of risk. Management reviews and approves these policies and procedures on a regular basis. A reporting system supplements the review process by providing management with frequent reports related to loan production, loan quality, concentrations of credit, loan delinquencies and nonperforming and potential problem loans. Commercial loans are underwritten after evaluating and understanding the borrower’s ability to operate profitably and prudently expand its business. The Company’s management examines current and projected cash flows to determine the ability of the borrower to repay their obligations as agreed. Commercial loans are primarily made based on the identified cash flows of the borrower and secondarily on the underlying collateral provided by the borrower. These cash flows, however, may not be as expected and the value of collateral securing the loans may fluctuate. Most commercial loans are secured by the assets being financed or other business assets such as accounts receivable or inventory and may incorporate a personal guarantee; however, some short term loans may be made on an unsecured basis. Additionally, our commercial loan portfolio includes loans made to customers in the energy industry, which is a complex, technical and cyclical industry. Experienced bankers with specialized energy lending experience originate our energy loans. Companies in this industry produce, extract, develop, exploit and explore for oil and natural gas. Loans are primarily collateralized with proven producing oil and gas reserves based on a technical evaluation of these reserves. At March 31, 2021 and December 31, 2020, there were approximately $202,145 and $205,496, of energy related loans outstanding, respectively. The Company has a mortgage warehouse purchase program providing mortgage inventory financing for residential mortgage loans originated by mortgage banker clients across a broad geographic scale. Proceeds from the sale of mortgages is the primary source of repayment for warehouse inventory financing via approved investor takeout commitments. These loans typically have a very short duration ranging between a few days to 15 days. In some cases, loans to larger mortgage originators may be financed for up to 60 days. These loans are reported as commercial loans since the loans are secured by notes receivable, not real estate. As of March 31, 2021 and December 31, 2020, mortgage warehouse purchase loans outstanding totaled $1,105,699 and $1,453,797, respectively. With the passage of the CARES Act Paycheck Protection Program (PPP), administered by the Small Business Administration (SBA), the Company has participated in originating loans to its customers through the program. PPP loans have terms of two Commercial real estate loans are subject to underwriting standards and processes similar to commercial loans. These loans are viewed primarily as cash flow loans and secondarily as loans secured by real estate. Commercial real estate lending typically involves higher loan principal amounts, and the repayment of these loans is generally largely dependent on the successful operation of the property or the business conducted on the property securing the loan. Commercial real estate loans may be more adversely affected by conditions in the real estate markets or in the general economy. The properties securing the Company’s commercial real estate portfolio are diverse in terms of type and geographic location. Management monitors the diversification of the portfolio on a quarterly basis by type and geographic location. Management also tracks the level of owner occupied property versus non-owner occupied property. At March 31, 2021, the portfolio consisted of approximately 28% of owner occupied property. Land and commercial land development loans are underwritten using feasibility studies, independent appraisal reviews and financial analysis of the developers or property owners. Generally, borrowers must have a proven track record of success. Commercial construction loans are generally based upon estimates of cost and value of the completed project. These estimates may not be accurate. Commercial construction loans often involve the disbursement of substantial funds with the repayment dependent on the success of the ultimate project. Sources of repayment for these loans may be pre-committed permanent financing or sale of the developed property. The loans in this portfolio are geographically diverse and due to the increased risk are monitored closely by management and the board of directors on a quarterly basis. Residential real estate and single-family interim construction loans are underwritten primarily based on borrowers’ credit scores, documented income and minimum collateral values. Relatively small loan amounts are spread across many individual borrowers, which minimizes risk in the residential portfolio. In addition, management evaluates trends in past dues and current economic factors on a regular basis. Agricultural loans are collateralized by real estate and/or agricultural-related assets. Agricultural real estate loans are primarily comprised of loans for the purchase of farmland. Loan-to-value ratios on loans secured by farmland generally do not exceed 80% and have amortization periods limited to twenty years. Agricultural non-real estate loans are generally comprised of term loans to fund the purchase of equipment, livestock and seasonal operating lines to grain farmers to plant and harvest corn and soybeans. Specific underwriting standards have been established for agricultural-related loans including the establishment of projections for each operating year based on industry developed estimates of farm input costs and expected commodity yields and prices. Operating lines are typically written for one year and secured by the crop and other farm assets as considered necessary. Agricultural loans carry significant credit risks as they involve larger balances concentrated with single borrowers or groups of related borrowers. In addition, repayment of such loans depends on the successful operation or management of the farm property securing the loan or for which an operating loan is utilized. Farming operations may be affected by adverse weather conditions such as drought, hail or floods that can severely limit crop yields. Consumer loans represent less than 1% of the outstanding total loan portfolio. Collateral consists primarily of automobiles and other personal assets. Credit score analysis is used to supplement the underwriting process. Most of the Company’s lending activity occurs within the State of Texas, primarily in the north, central and southeast Texas regions and the State of Colorado, specifically along the Front Range area. As of March 31, 2021, loans in the Colorado region represented about 27% of the total portfolio. A large percentage of the Company’s portfolio consists of commercial and residential real estate loans. As of March 31, 2021 and December 31, 2020, there were no concentrations of loans related to a single industry in excess of 10% of total loans. On January 1, 2021, the Company adopted ASU 2016-13, Financial Instruments - Credit Losses (Topic 326) (ASC 326). Under ASC 326, the allowance for credit losses is a valuation account that is deducted from the amortized cost basis of loans to present the net amount expected to be collected on the loans. Loans, or portions thereof, are charged off against the allowance when they are deemed uncollectible. Expected recoveries do not exceed the aggregate of amounts previously charged-off and expected to be charged-off. The amount of the allowance represents management's best estimate of current expected credit losses on loans considering available information relevant to assessing collectibility over the loans' contractual terms, adjusted for expected prepayments when appropriate. The contractual term excludes expected extensions, renewals and modifications unless either of the following applies: management has a reasonable expectation that a troubled debt restructuring will be executed with an individual borrower, or the extension or renewal options are included in the borrower contract and are not unconditionally cancellable by the Company. The Company's allowance balance is estimated using relevant available information, from internal and external sources, relating to past events, current conditions and reasonable and supportable forecasts. Historical credit loss experience provides the basis for the estimation of expected credit losses. Adjustments to historical loss information are made for differences in current loan-specific risk characteristics such as differences in underwriting standards, portfolio mix, credit quality, or term as well as for changes in environmental conditions, such as changes in unemployment rates, gross domestic product, property values or other relevant factors. The Company utilizes Moody’s Analytics economic forecast scenarios and assigns probability weighting to those scenarios which best reflect management’s views on the economic forecast. Management continually evaluates the allowance for credit losses based upon the factors noted above. Should any of the factors considered by management change, the Company’s estimate of credit losses could also change and would affect the level of future provision for credit losses. Portions of the allowance may be allocated for specific credits; however, the entire allowance is available for any credit that, in management’s judgment, should be charged off. While the calculation of the allowance for credit losses utilizes management’s best judgment and all the information available, the adequacy of the allowance for credit losses is dependent on a variety of factors beyond the Company’s control, including, among other things, the performance of the entire loan portfolio, the economy, changes in interest rates and the view of regulatory authorities towards loan classifications. The allowance for credit losses is measured on a collective basis for portfolios of loans when similar risk characteristics exist. Loans that do not share risk characteristics are evaluated for expected credit losses on an individual basis and excluded from the collective evaluation. For determining the appropriate allowance for credit losses on a collective basis, the loan portfolio is segmented into pools based upon similar risk characteristics and a lifetime loss-rate model is utilized. For modeling purposes, loan pools include: commercial and industrial, energy, commercial real estate - construction/land development, commercial real estate - owner occupied, commercial real estate - non-owner occupied, agricultural, residential real estate, HELOCs, single-family interim construction, and consumer and other. Management periodically reassesses each pool to ensure the loans within the pool continue to share similar characteristics and risk profiles and to determine whether further segmentation is necessary. The measurement of expected credit losses is impacted by loan/borrower attributes and certain macroeconomic variables. Management has determined that they are reasonably able to forecast the macroeconomic variables used in the modeling processes with an acceptable degree of confidence for a total of two years then encompassing a reversion process whereby the forecasted macroeconomic variables are reverted to their historical mean utilizing a rational, systematic basis. Management qualitatively adjusts model results for risk factors that are not considered within the modeling processes but are nonetheless relevant in assessing the expected credit losses within the loan pools. These qualitative factor (Q-Factor) adjustments may increase or decrease management's estimate of expected credit losses by a calculated percentage or amount based upon the estimated level of risk. Loans exhibiting unique risk characteristics and requiring an individual allowance are generally identified at the servicing officer level based on review of weekly past due reports and/or the loan officer’s communication with borrowers. In addition, the status of past due loans are routinely discussed within each lending region as well as credit committee meetings to determine if classification is warranted. The Company’s internal loan review department has implemented an internal risk-based loan review process to identify potential internally classified loans that supplements the independent external loan review. External loan reviews cover a wide range of the loan portfolio, including large lending relationships, specifically targeted loan types, and if applicable recently acquired loan portfolios. As such, the external loan review generally covers loans exceeding $3,000. These reviews include analysis of borrower’s financial condition, payment histories, review of loan documentation and collateral values to determine if a loan should be internally classified. Generally, once classified, an analysis is completed by the credit department to determine the amount of allocated allowance for credit loss required. Expected credit losses for collateral dependent loans, including loans where the borrower is experiencing financial difficulty but foreclosure is not probable, are based on the fair value of the collateral at the reporting date, adjusted for selling costs as appropriate. Prior to the adoption of ASU 2016-13, the allowance for credit losses on loans was a contra-asset valuation account established through a provision for loan losses charged to expense, which represented management’s best estimate of inherent losses that had been incurred within the existing portfolio of loans. The allowance for credit losses on loans included allowance allocations calculated in accordance with ASC Topic 310, Receivables, and allowance allocations calculated in accordance with ASC Topic 450, Contingencies. Following unprecedented declines caused by the pandemic and volatile energy prices, the Texas economy, specifically in the Company’s lending areas of north, central and southeast Texas, and the Colorado economy expanded at a moderate pace into the first quarter of 2021. Activity in the manufacturing and service sectors picked up in early February after stalling in January, while retail activity remained flat. Energy activity improved further. Overall, loan volume decreased slightly, though real estate lending continued to rise. Outlooks are generally positive, but uncertainty persisted with continued concerns about rising COVID-19 infection rates impacting the overall economic recovery mitigated slightly by optimism about the vaccine paving the way to a resumption of normal economic activity in 2021. The pandemic crisis has been impactful and the timing and magnitude of recovery cannot be predicted. The risk of loss associated with all segments of the portfolio could increase due to these factors. The economy and other risk factors are minimized by the Company’s underwriting standards, which include the following principles: 1) financial strength of the borrower including strong earnings, high net worth, significant liquidity and acceptable debt to worth ratio, 2) managerial business competence, 3) ability to repay, 4) loan to value, 5) projected cash flow and 6) guarantor financial statements as applicable. The following is a summary of the activity in the allowance for credit losses on loans by class for the three months ended March 31, 2021 and 2020: Commercial Commercial Residential Single-Family Agricultural Consumer Other Unallocated Total Three months ended March 31, 2021 Balance at beginning of period $ 27,311 $ 50,123 $ 6,786 $ 2,156 $ 337 $ 442 $ 242 $ 423 $ 87,820 Impact of adopting ASC 326 12,775 51,116 (2,255) 7,179 (178) (110) (224) (423) 67,880 Initial allowance on loans purchased with credit deterioration 4,328 8,567 140 — — — — — 13,035 Provision for credit losses 4,501 (5,932) (270) (1,007) (51) 36 223 — (2,500) Charge-offs (70) (301) — — — (18) (57) — (446) Recoveries 18 — — — — 3 17 — 38 Balance at end of period $ 48,863 $ 103,573 $ 4,401 $ 8,328 $ 108 $ 353 $ 201 $ — $ 165,827 Three months ended March 31, 2020 Balance at beginning of period $ 12,844 $ 33,085 $ 3,678 $ 1,606 $ 332 $ 226 $ 5 $ (315) $ 51,461 Provision for credit losses 5,053 1,733 759 307 13 28 131 357 8,381 Charge-offs (571) (735) — (82) — (9) (112) — (1,509) Recoveries 16 — — — — 18 36 — 70 Balance at end of period $ 17,342 $ 34,083 $ 4,437 $ 1,831 $ 345 $ 263 $ 60 $ 42 $ 58,403 The Company will charge-off that portion of any loan which management considers a loss. Commercial and real estate loans are generally considered for charge-off when exposure beyond collateral coverage is apparent and when no further collection of the loss portion is anticipated based on the borrower’s financial condition. The following table presents loans that were evaluated for expected credit losses on an individual basis and the related specific credit loss allocations, by loan class as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Loan Balance - Specific Allocations Loan Balance - Specific Allocations Commercial $ 44,933 $ 15,948 $ 39,298 $ 8,281 Commercial real estate, construction, land and land development 27,211 3,863 21,880 243 Residential real estate — — 2,550 — Single-family Interim construction — — — — Agricultural — — 613 — Consumer — — 42 — Other — — — — $ 72,144 $ 19,811 $ 64,383 $ 8,524 Nonperforming loans by loan class at March 31, 2021 (at amortized cost) and December 31, 2020 (at recorded investment), are summarized as follows: Commercial Commercial Residential Real Estate Single-Family Agricultural Consumer Other Total March 31, 2021 Nonaccrual loans (1) $ 32,912 $ 22,312 $ 2,289 $ — $ 551 $ 26 $ — $ 58,090 Loans past due 90 days and still accruing 316 — — — — — — 316 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) — 1,786 173 — — — — 1,959 $ 33,228 $ 24,098 $ 2,462 $ — $ 551 $ 26 $ — $ 60,365 December 31, 2020 (2) Nonaccrual loans $ 25,898 $ 20,072 $ 2,372 $ — $ 613 $ 42 $ — $ 48,997 Loans past due 90 days and still accruing 433 — — — — — — 433 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) — 1,808 178 — — — — 1,986 $ 26,331 $ 21,880 $ 2,550 $ — $ 613 $ 42 $ — $ 51,416 ____________ (1) There are $3,016 in loans on nonaccrual without an allowance for credit loss as of March 31, 2021. Additionally, no interest income was recognized on nonaccrual loans. No significant amounts of accrued interest was reversed during the three months ended March 31, 2021. (2) Excluded loans acquired with deteriorated credit quality under prior GAAP. The accrual of interest is discontinued on a loan when management believes that, after considering collection efforts and other factors, the borrower's financial condition is such that collection of interest is doubtful, as well as when required by regulatory provisions. Regulatory provisions would typically require the placement of a loan on non-accrual status if 1) principal or interest has been in default for a period of 90 days or more unless the loan is both well secured and in the process of collection or 2) full payment of principal and interest is not expected. All interest accrued but not collected for loans that are placed on nonaccrual status or charged-off is reversed against interest income. Cash collections on nonaccrual loans are generally credited to the loan receivable balance, and no interest income is recognized on those loans until the principal balance has been collected. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured. The restructuring of a loan is considered a “troubled debt restructuring” (TDR) if both 1) the borrower is experiencing financial difficulties and 2) the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, principal forgiveness, extending amortization and other actions intended to minimize potential losses. Modifications primarily relate to extending the amortization periods of the loans and interest rate concessions. The modifications during the reported periods did not materially impact the Company’s determination of the allowance for credit losses. The amortized cost basis and recorded investment in troubled debt restructurings, including those on nonaccrual, was $2,549 and $2,564 as of March 31, 2021 and December 31, 2020, respectively. Following is a summary of loans modified under troubled debt restructurings during the three months ended March 31, 2021 and 2020: Commercial Commercial Residential Single-Family Agricultural Consumer Other Total Troubled debt restructurings during the three months ended March 31, 2021 Number of contracts 1 — — — — — — 1 Pre-restructuring outstanding recorded investment $ 49 $ — $ — $ — $ — $ — $ — $ 49 Post-restructuring outstanding recorded investment $ 44 $ — $ — $ — $ — $ — $ — $ 44 Troubled debt restructurings during the three months ended March 31, 2020 Number of contracts — 1 — — — — — 1 Pre-restructuring outstanding recorded investment $ — $ 1,517 $ — $ — $ — $ — $ — $ 1,517 Post-restructuring outstanding recorded investment $ — $ 1,517 $ — $ — $ — $ — $ — $ 1,517 At March 31, 2021 and 2020, there were no loans modified under troubled debt restructurings during the previous twelve month period that subsequently defaulted during the three months ended March 31, 2021 and 2020, respectively. At March 31, 2021 and 2020, the Company had no commitments to lend additional funds to any borrowers with loans whose terms have been modified under troubled debt restructurings. Under ASC Subtopic 310-40 and federal banking agencies interagency guidance, certain short-term loan modifications made on a good faith basis in response to COVID-19 (as defined by the guidance) are not considered TDRs. Additionally, under section 4013 of the CARES Act, and as amended, banks may elect to suspend the requirement for certain loan modifications to be categorized as a TDR. In response to the COVID-19 pandemic, the Company has implemented prudent modifications allowing for primarily short-term payment deferrals or other payment relief to borrowers with pandemic-related economic hardships, where appropriate, that complies with the above guidance. As such, the Company's TDR loans noted above do not include loans that are modifications to borrowers impacted by COVID-19. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. The following table presents information regarding the aging of past due loans by loan class as of March 31, 2021 (at amortized cost) and as of December 31, 2020 (at recorded investment): Loans Loans Total Past Current Total March 31, 2021 Commercial $ 1,185 $ 20,422 $ 21,607 $ 3,575,047 $ 3,596,654 Commercial real estate, construction, land and land development 6,223 15,844 22,067 7,378,636 7,400,703 Residential real estate 3,175 1,357 4,532 1,305,839 1,310,371 Single-family interim construction 355 — 355 312,620 312,975 Agricultural 37 — 37 74,783 74,820 Consumer 91 21 112 74,811 74,923 Other — — — 311 311 $ 11,066 $ 37,644 $ 48,710 $ 12,722,047 $ 12,770,757 December 31, 2020 (1) Commercial $ 3,243 $ 13,227 $ 16,470 $ 3,846,810 $ 3,863,280 Commercial real estate, construction, land and land development 2,453 16,790 19,243 7,152,247 7,171,490 Residential real estate 5,169 1,028 6,197 1,341,587 1,347,784 Single-family interim construction — — — 326,575 326,575 Agricultural — 1 1 84,896 84,897 Consumer 86 41 127 66,810 66,937 Other — — — 346 346 10,951 31,087 42,038 12,819,271 12,861,309 Acquired with deteriorated credit quality 624 3,219 3,843 210,943 214,786 $ 11,575 $ 34,306 $ 45,881 $ 13,030,214 $ 13,076,095 ____________ (1) Presented under prior GAAP. The Company’s internal classified report is segregated into the following categories: 1) Pass/Watch, 2) Special Mention, 3) Substandard and 4) Doubtful. The loans placed in the Pass/Watch category reflect the Company’s opinion that the loans reflect potential weakness that requires monitoring on a more frequent basis. The loans in the Special Mention category reflect the Company’s opinion that the credit contains weaknesses which represent a greater degree of risk and warrant extra attention. These loans are reviewed monthly by officers and senior management to determine if a change in category is warranted. The loans placed in the Substandard category are considered to be potentially inadequately protected by the current debt service capacity of the borrower and/or the pledged collateral. These credits, even if apparently protected by collateral value, have shown weakness related to adverse financial, managerial, economic, market or political conditions, which may jeopardize repayment of principal and interest and may be considered impaired. There is a possibility that some future loss could be sustained by the Company if such weakness is not corrected. The Doubtful category includes loans that are in default or principal exposure is probable and the possibility of loss is extremely high. The following summarizes the amortized cost basis of loans by year of origination/renewal and credit quality indicator by class of loan as of March 31, 2021: Revolving Loans Converted to Term Loans Term Loans by Year of Origination Revolving Loans March 31, 2021 2021 2020 2019 2018 2017 Prior Total Commercial Pass $ 282,123 $ 937,698 $ 159,944 $ 138,458 $ 128,778 $ 156,849 $ 1,571,377 $ 3,269 $ 3,378,496 Pass/Watch 472 1,922 1,650 10,446 9,389 99 44,719 1,336 70,033 Special Mention — 3,938 19,103 7,959 443 1,020 3,023 — 35,486 Substandard 13,148 851 33,434 8,178 9,262 17,383 18,474 — 100,730 Doubtful — — 1,745 — — — 10,164 — 11,909 Total commercial $ 295,743 $ 944,409 $ 215,876 $ 165,041 $ 147,872 $ 175,351 $ 1,647,757 $ 4,605 $ 3,596,654 Commercial real estate Pass $ 396,430 $ 1,440,420 $ 968,483 $ 835,598 $ 746,267 $ 1,005,653 $ 62,697 $ 336 $ 5,455,884 Pass/Watch 47,331 47,901 70,961 81,980 34,548 73,083 1 499 356,304 Special Mention 7,960 54,141 40,520 77,624 52,831 54,845 — — 287,921 Substandard 16,617 37,704 2,418 3,128 1,593 31,210 1,574 — 94,244 Doubtful — — — — — — — — — Total commercial real estate $ 468,338 $ 1,580,166 $ 1,082,382 $ 998,330 $ 835,239 $ 1,164,791 $ 64,272 $ 835 $ 6,194,353 Commercial construction, land and land development Pass $ 151,932 $ 365,287 $ 310,392 $ 177,927 $ 25,629 $ 20,017 $ 9,647 $ — $ 1,060,831 Pass/Watch 1,984 4,659 28,682 18,227 10,397 272 — — 64,221 Special Mention — 16,205 15,981 — 9,999 — — — 42,185 Substandard 11,593 3,990 1,435 20,068 30 1,997 — — 39,113 Doubtful — — — — — — — — — Total commercial construction, land and land development $ 165,509 $ 390,141 $ 356,490 $ 216,222 $ 46,055 $ 22,286 $ 9,647 $ — $ 1,206,350 Residential real estate Pass $ 77,163 $ 343,414 $ 270,486 $ 167,961 $ 127,440 $ 242,257 $ 59,961 $ 1,462 $ 1,290,144 Pass/Watch 649 594 1,419 423 548 5,860 65 — 9,558 Special Mention 1,398 1,154 — 133 260 1,174 230 — 4,349 Substandard 189 648 614 1,013 842 2,957 57 — 6,320 Doubtful — — — — — — — — — Total residential real estate $ 79,399 $ 345,810 $ 272,519 $ 169,530 $ 129,090 $ 252,248 $ 60,313 $ 1,462 $ 1,310,371 Revolving Loans Converted to Term Loans Term Loans by Year of Origination Revolving Loans March 31, 2021 2021 2020 2019 2018 2017 Prior Total Single-family interim construction Pass $ 62,725 $ 209,338 $ 26,092 $ 363 $ — $ 380 $ 13,373 $ — $ 312,271 Pass/Watch — 704 — — — — — — 704 Special Mention — — — — — — — — — Substandard — — — — — — — — — Doubtful — — — — — — — — — Total single-family interim construction $ 62,725 $ 210,042 $ 26,092 $ 363 $ — $ 380 $ 13,373 $ — $ 312,975 Agricultural Pass $ 3,041 $ 21,531 $ 4,899 $ 10,382 $ 14,889 $ 6,620 $ 6,547 $ — $ 67,909 Pass/Watch — 552 1,698 66 — 146 2,509 — 4,971 Special Mention — — — — 1,000 — 336 — 1,336 Substandard 2 — — — — 602 — — 604 Doubtful — — — — — — — — — Total agricultural $ 3,043 $ 22,083 $ 6,597 $ 10,448 $ 15,889 $ 7,368 $ 9,392 $ — $ 74,820 Consumer Pass $ 2,486 $ 13,632 $ 3,893 $ 1,911 $ 758 $ 640 $ 51,464 $ 50 $ 74,834 Pass/Watch — — — — 4 — — — 4 Special Mention — — — — — — — — — Substandard — 32 7 — 13 33 — — 85 Doubtful — — — — — — — — — Total consumer $ 2,486 $ 13,664 $ 3,900 $ 1,911 $ 775 $ 673 $ 51,464 $ 50 $ 74,923 Other Pass $ 311 $ — $ — $ — $ — $ — $ — $ — $ 311 Pass/Watch — — — — — — — — — Special Mention — — — — — — — — — Substandard — — — — — — — — — Doubtful — — — — — — — — — Total other $ 311 $ — $ — $ — $ — $ — $ — $ — $ 311 A summary of loans at recorded investment by credit quality indicator by class presented under prior GAAP as of December 31, 2020, is as follows: Pass Pass/ Special Mention Substandard Doubtful Total December 31, 2020 Commercial $ 3,700,626 $ 55,960 $ 38,186 $ 97,403 $ 10,091 $ 3,902,266 Commercial real estate, construction, land and land development 6,504,933 352,910 360,963 123,671 — 7,342,477 Residential real estate 1,332,757 6,296 5,726 7,686 — 1,352,465 Single-family interim construction 323,800 2,775 — — — 326,575 Agricultural 76,951 6,194 1,205 664 — 85,014 Consumer 66,854 8 — 90 — 66,952 Other 346 — — — — 346 $ 12,006,267 $ 424,143 $ 406,080 $ 229,514 $ 10,091 $ 13,076,095

Off-Balance Sheet Arrangements,

Off-Balance Sheet Arrangements, Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Off-Balance Sheet Arrangements, Commitments and Contingencies	Off-Balance Sheet Arrangements, Commitments and Contingencies Financial Instruments with Off-Balance Sheet Risk The Company is a party to financial instruments with off-balance sheet risk in the normal course of business to meet the financing needs of its customers. The commitments involve, to varying degrees, elements of credit and interest rate risk in excess of the amount recognized in the balance sheet. The Company’s exposure to credit loss in the event of nonperformance by the other party to the financial instrument for commitments to extend credit is represented by the contractual amount of this instrument. The Company uses the same credit policies in making commitments and conditional obligations as it does for on-balance sheet instruments. At March 31, 2021 and December 31, 2020, the approximate amounts of these financial instruments were as follows: March 31, December 31, 2021 2020 Commitments to extend credit $ 2,338,297 $ 2,268,216 Standby letters of credit 25,849 25,917 $ 2,364,146 $ 2,294,133 Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company evaluates each customer’s credit worthiness on a case-by-case basis. The amount of collateral obtained if deemed necessary by the Company upon extension of credit is based on management’s credit evaluation of the counterparty. Collateral held varies but may include accounts receivable, inventory, farm crops, property, plant and equipment and income-producing commercial properties. Letters of credit are written conditional commitments used by the Company to guarantee the performance of a customer to a third party. The Company’s policies generally require that letter of credit arrangements contain security and debt covenants similar to those contained in loan arrangements. In the event the customer does not perform in accordance with the terms of the agreement with the third party, the Company would be required to fund the commitment. The maximum potential amount of future payments the Company could be required to make is represented by the contractual amount shown in the table above. If the commitment is funded, the Company would be entitled to seek recovery from the customer. Allowance For Credit Losses on Off-Balance Sheet Credit Exposures The allowance for credit losses on off-balance-sheet credit exposures is calculated under ASC 326, representing expected credit losses over the contractual period for which the Company is exposed to credit risk resulting from a contractual obligation to extend credit. Off-balance sheet credit exposures primarily consist of amounts available under outstanding lines of credit and letters of credit detailed in the table above. The allowance for credit losses on off-balance sheet credit exposures is estimated by loan segment at each balance sheet date using the same methodologies as portfolio loans, taking into consideration the likelihood that funding will occur based on historical utilization rates. The allowance is included in other liabilities on the Company’s consolidated balance sheets. The allowance for credit losses on off-balance-sheet commitments were as follows: Three Months Ended March 31, 2021 2020 Balance at beginning of period $ — $ — Impact of CECL adoption 1,113 — Provision for off-balance sheet credit exposure — — Balance at end of period $ 1,113 $ — Litigation The Company is involved in certain legal actions arising from normal business activities. Management believes that the outcome of such proceedings will not materially affect the financial position, results of operations or cash flows of the Company. A legal proceeding that the Company believes could become material is described below.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense for the three months ended March 31, 2021 and 2020 was as follows: Three Months Ended March 31, 2021 2020 Income tax expense for the period $ 15,745 $ 10,836 Effective tax rate 20.8 % 19.7 % The effective tax rates for 2021 and 2020 differ from the statutory federal tax rate of 21% largely due to tax exempt interest income earned on certain investment securities and loans, the nontaxable earnings on bank owned life insurance, nondeductible compensation, acquisition-related expenses, and state income tax. In addition, the lower effective tax rate for the three months ended March 31, 2020 is a result of a tax benefit recorded due to the net operating loss carryback provision allowed through the enactment of the CARES Act.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. ASC Topic 820, Fair Value Measurements and Disclosures , establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: Level 1 Inputs – Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 Inputs – Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. Level 3 Inputs – Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. The Company elected the fair value option for certain residential mortgage loans held for sale in accordance with ASC 825, Financial Instruments. This election allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . The Company has not elected the fair value option for other residential mortgage loans held for sale primarily because they are not economically hedged using derivative instruments. See below and Note 8, Derivative Financial Instruments , for additional information. Assets and Liabilities Measured on a Recurring Basis The following table represents assets and liabilities reported on the consolidated balance sheets at their fair value on a recurring basis as of March 31, 2021 and December 31, 2020 by level within the ASC Topic 820 fair value measurement hierarchy: Fair Value Measurements at Reporting Date Using Assets/ Quoted Prices Significant Significant March 31, 2021 Assets: Investment securities available for sale: U.S. treasuries $ 34,452 $ — $ 34,452 $ — Government agency securities 289,640 — 289,640 — Obligations of state and municipal subdivisions 387,856 — 387,856 — Corporate bonds 28,995 — 28,995 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 565,814 — 565,814 — Other securities 1,200 — 1,200 — Loans held for sale, fair value option elected (1) 53,930 — 53,930 — Derivative financial instruments: Interest rate lock commitments 2,158 — 2,158 — Forward mortgage-backed securities trades 787 — 787 — Loan customer counterparty 12,427 — 12,427 — Financial institution counterparty 1,372 — 1,372 — Liabilities: Derivative financial instruments: Interest rate lock commitments 52 — 52 — Forward mortgage-backed securities trades 9 — 9 — Loan customer counterparty 1,291 — 1,291 — Financial institution counterparty 12,952 — 12,952 — December 31, 2020 Assets: Investment securities available for sale: U.S. treasuries $ 44,708 $ — $ 44,708 $ — Government agency securities 249,017 — 249,017 — Obligations of state and municipal subdivisions 393,165 — 393,165 — Corporate bonds 22,102 — 22,102 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 443,501 — 443,501 — Other securities 1,200 — 1,200 — Loans held for sale, fair value option elected (1) 71,769 — 71,769 — Derivative financial instruments: Interest rate lock commitments 3,515 — 3,515 — Loan customer counterparty 20,159 — 20,159 — Liabilities: Derivative financial instruments: Forward mortgage-backed securities trades 568 — 568 — Financial institution counterparty 21,306 — 21,306 — ____________ (1) At March 31, 2021 and December 31, 2020, loans held for sale for which the fair value option was elected had an aggregate outstanding principal balance of $53,030 and $68,670, respectively. There were no mortgage loans held for sale under the fair value option that were 90 days or greater past due or on nonaccrual at March 31, 2021. A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. Investment securities Securities classified as available for sale are reported at fair value utilizing Level 1 and Level 2 inputs. Securities are classified within Level 1 when quoted market prices are available in an active market. Inputs include securities that have quoted prices in active markets for identical assets. For securities utilizing Level 2 inputs, the Company obtains fair value measurements from an independent pricing service. The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury and other yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Loans held for sale Certain mortgage loans held for sale are measured at fair value on a recurring basis due to the Company's election to adopt fair value accounting treatment for those loans originated for which the Company has entered into certain derivative financial instruments as part of its mortgage banking and related risk management activities. These instruments include interest rate lock commitments and mandatory forward commitments to sell these loans to investors known as forward mortgage-backed securities trades. This election allows for a more effective offset of the changes in fair values of the assets and the mortgage related derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . Mortgage loans held for sale, for which the fair value option was elected, which are sold on a servicing released basis, are valued using a market approach by utilizing either: (i) the fair value of securities backed by similar mortgage loans, adjusted for certain factors to approximate the fair value of a whole mortgage loan, including the value attributable to mortgage servicing and credit risk, (ii) current commitments to purchase loans or (iii) recent observable market trades for similar loans, adjusted to credit risk and other individual loan characteristics. As these prices are derived from market observable inputs, the Company classifies these valuations as Level 2 in the fair value disclosures. For mortgage loans held for sale for which the fair value option was elected, the earned current contractual interest payment is recognized in interest income, loan origination costs and fees on fair value option loans are recognized in earnings as incurred and not deferred. The Company has no continuing involvement in any residential mortgage loans sold. Derivatives The estimated fair values of interest rate lock commitments utilize current secondary market prices for underlying loans and estimated servicing value with similar coupons, maturity and credit quality, subject to the anticipated loan funding probability (pull-through rate). The fair value of interest rate lock commitments is subject to change primarily due to changes in interest rates and the estimated pull-through rate. These commitments are classified as Level 2 in the fair value disclosures, as the valuations are based on observable market inputs. Forward mortgage-backed securities trades are exchange-traded or traded within highly active dealer markets. In order to determine the fair value of these instruments, the Company utilized the exchange price or dealer market price for the particular derivative contract; therefore these contracts are classified as Level 2. The estimated fair values are subject to change primarily due to changes in interest rates. The Company also enters into certain interest rate derivative positions that are not designated as hedging instruments. The estimated fair value of these commercial loan interest rate swaps are obtained from a pricing service that provides the swaps' unwind value (Level 2 inputs). See Note 8, Derivative Financial Instruments , for more information. Assets and Liabilities Measured on a Nonrecurring Basis In accordance with ASC Topic 820, certain assets and liabilities are measured at fair value on a nonrecurring basis; that is, the assets and liabilities are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). The following table presents the assets carried on the consolidated balance sheet by caption and by level in the fair value hierarchy at March 31, 2021 and December 31, 2020, for which a nonrecurring change in fair value has been recorded: Fair Value Measurements at Reporting Date Using Assets Quoted Prices Significant Significant Period Ended March 31, 2021 Assets: Individually evaluated loans $ 12,481 $ — $ — $ 12,481 $ 2,773 December 31, 2020 Assets: Individually evaluated loans $ 16,903 $ — $ — $ 16,903 $ 13,041 Individually evaluated loans (loans which are not expected to repay all principal and interest amounts due in accordance with the original contractual terms) are measured at an observable market price (if available) or at the fair value of the loan’s collateral (if collateral dependent). Fair value of the loan’s collateral is determined by appraisals or independent valuation, which is then adjusted for the estimated costs related to liquidation of the collateral. Management’s ongoing review of appraisal information may result in additional discounts or adjustments to valuation based upon more recent market sales activity or more current appraisal information derived from properties of similar type and/or locale. In addition, management's discounting criteria may vary for loans secured by non-real estate collateral such as inventory, oil and gas reserves, accounts receivable, equipment or other business assets. Therefore, the Company has categorized its individually evaluated loans as Level 3. Other real estate is measured at fair value on a nonrecurring basis (upon initial recognition or subsequent impairment). Other real estate is classified within Level 3 of the valuation hierarchy. When transferred from the loan portfolio, other real estate is adjusted to fair value less estimated selling costs and is subsequently carried at the lower of carrying value or fair value less estimated selling costs. The fair value is determined using an external appraisal process, discounted based on internal criteria. Therefore, the Company has categorized its other real estate as Level 3. There was no other real estate owned remeasured during the three months ended March 31, 2021 and the year ended December 31, 2020. In addition, mortgage loans held for sale not recorded under the fair value option are required to be measured at the lower of cost or fair value. The fair value of these loans is based upon binding quotes or bids from third party investors. As of March 31, 2021 and December 31, 2020, all mortgage loans held for sale not recorded under the fair value option were recorded at cost. Fair Value of Financial Instruments not Recorded at Fair Value The carrying amount, estimated fair value and the level of the fair value hierarchy of the Company’s financial instruments that are reported at amortized cost on the Company's consolidated balance sheets were as follows at March 31, 2021 and December 31, 2020: Fair Value Measurements at Reporting Date Using Carrying Estimated Quoted Prices Significant Significant March 31, 2021 Financial assets: Cash and cash equivalents $ 2,416,870 $ 2,416,870 $ 2,416,870 $ — $ — Certificates of deposit held in other banks 4,482 4,569 — 4,569 — Loans held for sale, at cost 3,869 3,963 — 3,963 — Loans, net 12,604,930 12,809,647 — — 12,809,647 FHLB of Dallas stock and other restricted stock 20,338 20,338 — 20,338 — Accrued interest receivable 59,896 59,896 — 59,896 — Financial liabilities: Deposits 14,803,792 14,810,771 — 14,810,771 — Accrued interest payable 3,654 3,654 — 3,654 — FHLB advances 375,000 366,583 — 366,583 — Other borrowings 308,350 327,350 — 327,350 — Junior subordinated debentures 54,072 41,292 — 41,292 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — — December 31, 2020 Financial assets: Cash and cash equivalents $ 1,813,987 $ 1,813,987 $ 1,813,987 $ — $ — Certificates of deposit held in other banks 4,482 4,595 — 4,595 — Loans held for sale, at cost 10,878 11,138 — 11,138 — Loans, net 12,978,238 13,093,698 — — 13,093,698 FHLB of Dallas stock and other restricted stock 20,305 20,305 — 20,305 — Accrued interest receivable 60,581 60,581 — 60,581 — Financial liabilities: Deposits 14,398,927 14,407,596 — 14,407,596 — Accrued interest payable 7,397 7,397 — 7,397 — FHLB advances 375,000 371,175 — 371,175 — Other borrowings 312,175 327,150 — 327,150 — Junior subordinated debentures 54,023 42,624 — 42,624 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — — The methods and assumptions used by the Company in estimating fair values of financial instruments as disclosed herein in accordance with ASC Topic 825, Financial Instruments , other than for those measured at fair value on a recurring and nonrecurring basis discussed above, are as follows: Cash and cash equivalents: The carrying amounts of cash and cash equivalents approximate their fair value. Certificates of deposit held in other banks: The fair value of certificates of deposit held in other banks is based upon current market rates. Loans held for sale, at cost: The fair value of loans held for sale is determined based upon commitments on hand from investors. Loans: A discounted cash flow model is used to estimate the fair value of the loans. The discounted cash flow approach models the credit losses directly in the projected cash flows, applying various assumptions regarding credit, interest and prepayment risks for the loans based on loan types, payment types and fixed or variable classifications. Federal Home Loan Bank of Dallas and other restricted stock: The carrying value of restricted securities such as stock in the Federal Home Loan Bank of Dallas and Independent Bankers Financial Corporation approximates fair value. Deposits: The fair values disclosed for demand deposits are, by definition, equal to the amount payable on demand at the reporting date (that is their carrying amounts). The carrying amounts of variable-rate certificates of deposit (CDs) approximate their fair values at the reporting date. Fair values for fixed-rate CDs are estimated using a discounted cash flow calculation that applies interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities on time deposits. Federal Home Loan Bank advances, line of credit and federal funds purchased: The fair value of advances maturing within 90 days approximates carrying value. Fair value of other advances is based on the Company’s current borrowing rate for similar arrangements. Other borrowings: The estimated fair value approximates carrying value for short-term borrowings. The fair value of private subordinated debentures are based upon prevailing rates on similar debt in the market place. The subordinated debentures that are publicly traded are valued based on indicative bid prices based upon market pricing observations in the current market. Junior subordinated debentures: The fair value of junior subordinated debentures is estimated using discounted cash flow analyses based on the published Bloomberg US Financials BB rated corporate bond index yield. Accrued interest: The carrying amounts of accrued interest approximate their fair values. Off-balance sheet instruments: Fair values for off-balance sheet, credit-related financial instruments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the counterparties' credit standing. The fair value of commitments is not material.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments The Company enters into certain derivative financial instruments as part of its hedging strategy. These financial instruments are not designated as hedging instruments and are used for asset and liability management related to the Company's mortgage banking activities and commercial customers' financing needs. All derivatives are carried at fair value in either other assets or other liabilities. Through the normal course of business, the Company enters into interest rate lock commitments with consumers to originate mortgage loans at a specified interest rate. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by the Company. The Company manages the changes in fair value associated with changes in interest rates related to interest rate lock commitments by using forward sold commitments known as forward mortgage-backed securities trades. These instruments are typically entered into at the time the interest rate lock commitment is made. The Company also offers certain derivatives products, primarily interest rate swaps, directly to qualified commercial banking customers to facilitate their risk management strategies. The interest rate swap derivative positions relate to transactions in which the Company enters into an interest rate swap with a customer, while at the same time entering into an offsetting interest rate swap with another financial institution. An interest rate swap transaction allows customers to effectively convert a variable rate loan to a fixed rate. In connection with each swap, the Company agrees to pay interest to the customer on a notional amount at a variable interest rate and receive interest from the customer on a similar notional amount at a fixed interest rate. At the same time, the Company agrees to pay another financial institution the same fixed interest rate on the same notional amount and receive the same variable interest rate on the same notional amount. The following table provides the outstanding notional balances and fair values of outstanding derivative positions at March 31, 2021 and December 31, 2020: Outstanding Notional Balance Asset Derivative Liability Derivative March 31, 2021 Interest rate lock commitments $ 90,496 $ 2,158 $ 52 Forward mortgage-backed securities trades 80,000 787 9 Commercial loan interest rate swaps: Loan customer counterparty 323,760 12,427 1,291 Financial institution counterparty 323,760 1,372 12,952 December 31, 2020 Interest rate lock commitments $ 116,795 $ 3,515 $ — Forward mortgage-backed securities trades 104,000 — 568 Commercial loan interest rate swaps: Loan customer counterparty 335,370 20,159 — Financial institution counterparty 335,370 — 21,306 The commercial loan customer counterparty weighted average received and paid interest rates for interest rate swaps outstanding were as follows: Weighted Average Interest Rate March 31, 2021 December 31, 2020 Received Paid Received Paid Loan customer counterparty 4.08 % 2.28 % 4.08 % 2.32 % The credit exposure related to interest rate swaps is limited to the net favorable value of all swaps by each counterparty, which was approximately $13,799 at March 31, 2021. In some cases collateral may be required from the counterparties involved if the net value of the derivative instruments exceeds a nominal amount. Collateral levels are monitored and adjusted on a regular basis for changes in interest rate swap values. At March 31, 2021, cash of $23,293 and securities of $6,404 were pledged as collateral for these derivatives. The Company has entered into credit risk participation agreements with financial institution counterparties for interest rate swaps related to loans in which the Company is either a participant or a lead bank. Risk participation agreements entered into as a participant bank provide credit protection to the financial institution counterparty should the borrower fail to perform on its interest rate derivative contract with that financial institution. The Company is party to one risk participation agreement as a participant bank having a notional amount of $5,510 at March 31, 2021. Risk participation agreements entered into as the lead bank provide credit protection to the Company should the borrower fail to perform on its interest rate derivative contract. The Company is party to one risk participation agreement as the lead bank having a notional amount of $9,541 at March 31, 2021. The changes in the fair value of interest rate lock commitments and the forward sales of mortgage-backed securities are recorded in mortgage banking revenue. These gains and losses were not attributable to instrument-specific credit risk. For interest rate swaps, because the Company acts as an intermediary for our customer, changes in the fair value of the underlying derivative contracts substantially offset each other and do not have a material impact on the results of operations. Income (loss) for the three months ended March 31, 2021 and 2020 was as follows: Three Months Ended March 31, 2021 2020 Derivatives not designated as hedging instruments Interest rate lock commitments $ (1,409) $ 551 Forward mortgage-backed securities trades 1,346 (1,252)

Stock Awards

Stock Awards	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock Awards	Stock AwardsThe Company grants common stock awards to certain employees of the Company. In connection with the Company's initial public offering in April 2013, the Board of Directors adopted the 2013 Equity Incentive Plan (2013 Plan). All stock awards issued under expired plans prior to 2013 are fully vested. Under the 2013 Plan, the Compensation Committee may grant awards to certain employees of the Company in the form of restricted stock, restricted stock rights, restricted stock units, qualified and nonqualified stock options, performance share awards and other equity-based awards. The 2013 Plan, as amended, has 2,300,000 reserved shares of common stock to be awarded by the Company’s compensation committee. As of March 31, 2021, there were 1,071,629 shares remaining available for grant for future awards. The shares currently issued under the 2013 Plan are restricted stock awards and performance stock units. Restricted stock awarded to employees vest evenly over the required employment period, generally ranging from one three four Restricted Stock Awards The following table summarizes the activity in nonvested restricted stock awards for the three months ended March 31, 2021 and 2020: Restricted Stock Awards Number of Weighted Average Nonvested shares, December 31, 2020 468,800 $ 49.01 Granted during the period 83,494 63.36 Vested during the period (106,107) 56.51 Forfeited during the period (4,506) 53.26 Nonvested shares, March 31, 2021 441,681 $ 49.88 Nonvested shares, December 31, 2019 284,861 $ 58.63 Granted during the period 94,177 53.48 Vested during the period (78,599) 57.94 Nonvested shares, March 31, 2020 300,439 $ 57.19 Compensation expense related to these awards is recorded based on the fair value of the award at the date of grant and totaled $2,496 and $1,882 for the three months ended March 31, 2021 and 2020, respectively. Compensation expense is recorded in salaries and employee benefits in the accompanying consolidated statements of income. At March 31, 2021, future compensation expense is estimated to be $18,378 and will be recognized over a remaining weighted average period of 2.55 years. The fair value of common stock awards that vested during the three months ended March 31, 2021 and 2020 was $6,875 and $4,198, respectively. The Company has recorded $(194) and $80 in excess tax (benefit) expense on vested restricted stock to income tax expense for the three months ended March 31, 2021 and 2020, respectively. There were no modifications of stock agreements during the three months ended March 31, 2021 and 2020 that resulted in significant additional incremental compensation costs. At March 31, 2021, the future vesting schedule of the nonvested restricted stock awards is as follows: First year 174,575 Second year 131,015 Third year 83,160 Fourth year 52,731 Fifth year 200 Total nonvested shares 441,681 Performance Stock Units Performance stock units represent shares potentially issuable in the future. The number of shares issued is based upon the measure of the Company's achievement of its relative adjusted return on average tangible common equity, as defined by the Company, over the award's performance period as compared to an identified peer group's achievement over the same performance period. The number of shares issuable under each performance award is the product of the award target and the award payout percentage for the given level of achievement which ranges from 0% to 150% of the target. The following table summarizes the activity in nonvested performance stock units at target award level for the three months ended March 31, 2021: Performance-based Restricted Stock Units Number of Weighted Average Nonvested shares, December 31, 2020 89,300 $ 38.29 Granted during the period 20,198 62.58 Nonvested shares, March 31, 2021 109,498 $ 42.77 Compensation expense related to performance stock units is estimated each period based on the fair value of the target stock unit at the grant date and the most probable level of achievement of the performance condition, adjusted for the passage of time within the vesting periods of the awards. As of March 31, 2021, the unrecognized compensation expense assuming the target attainment was $3,964, while the maximum payout rate was $6,315. The remaining performance period over which the expense will be recognized is 3.13 years. Compensation expense related to these awards was $710 for the three months ended March 31, 2021.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Regulatory Matters	Regulatory Matters Under banking law, there are legal restrictions limiting the amount of dividends the Bank can declare. Approval of the regulatory authorities is required if the effect of dividends declared would cause the regulatory capital of the Bank to fall below specified minimum levels. For state banks, subject to regulatory capital requirements, payment of dividends is generally allowed to the extent of net profits. The Company (on a consolidated basis) and the Bank are subject to various regulatory capital requirements administered by federal and state banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s consolidated financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Company and the Bank must meet specific capital guidelines that involve quantitative measures of assets, liabilities and certain off-balance sheet items as calculated under regulatory accounting practices. The capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings and other factors. Tier 2 capital for the Company includes permissible portions of the Company's subordinated notes. The permissible portion of qualified subordinated notes decreases 20% per year during the final five years of the term of the notes. The Company is subject to the Basel III regulatory capital framework (the Basel III Capital Rules). The Basel III Capital Rules require that the Company maintain a 2.5% capital conservation buffer above the minimum risk-based capital adequacy requirements. The capital conservation buffer is designed to absorb losses during periods of economic stress and requires increased capital levels for the purpose of capital distributions and other payments. Failure to meet the full amount of the buffer will result in restrictions on the Company's ability to make capital distributions, including dividend payments and stock repurchases and to pay discretionary bonuses to executive officers. As discussed in Note 1 - Summary of Significant Accounting Policies , in connection with the adoption of ASC 326, the Company recognized an after-tax cumulative effect reduction to retained earnings of $53,880 on January 1, 2021. In February 2019, the federal bank regulatory agencies issued a final rule that revised certain capital regulations under CECL and included a transition option that allows banking organizations to phase in, over a three-year period, the day-one adverse effects of CECL on their regulatory capital ratios (three-year transition option). The Company elected to adopt the three-year transition option and the deferral has been applied in the March 31, 2021 capital ratios presented below. Quantitative measures established by regulation to ensure capital adequacy require the Company and the Bank to maintain minimum amounts and ratios (set forth in the table below) of total, Common Equity Tier 1 (CET1) and Tier 1 capital (as defined in the regulations) to risk weighted assets (as defined), and of Tier 1 capital (as defined) to average assets (as defined). Management believes, as of March 31, 2021 and December 31, 2020, the Company and the Bank meet all capital adequacy requirements to which they are subject, including the capital buffer requirement. As of March 31, 2021 and December 31, 2020, the Bank’s capital ratios exceeded those levels necessary to be categorized as “well capitalized” under the regulatory framework for prompt corrective action. To be categorized as “well capitalized,” the Bank must maintain minimum total risk based, CET1, Tier 1 risk based and Tier 1 leverage ratios as set forth in the table. There are no conditions or events that management believes have changed the Bank’s category. The following table presents actual capital amounts and required ratios under Basel III Capital Rules for the Company and Bank as of March 31, 2021 and December 31, 2020. Actual Minimum Capital To Be Well Capitalized Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio March 31, 2021 Total capital to risk weighted assets: Consolidated $ 1,874,814 14.13 % $ 1,393,602 10.50 % N/A N/A Bank 1,904,255 14.35 1,393,159 10.50 $ 1,326,819 10.00 % Tier 1 capital to risk weighted assets: Consolidated 1,507,307 11.36 1,128,154 8.50 N/A N/A Bank 1,802,748 13.59 1,127,796 8.50 1,061,455 8.00 Common equity tier 1 to risk weighted assets: Consolidated 1,451,707 10.94 929,068 7.00 N/A N/A Bank 1,802,748 13.59 928,773 7.00 862,432 6.50 Tier 1 capital to average assets: Consolidated 1,507,307 9.01 668,972 4.00 N/A N/A Bank 1,802,748 10.78 668,786 4.00 835,983 5.00 December 31, 2020 Total capital to risk weighted assets: Consolidated $ 1,825,661 13.32 % $ 1,438,939 10.50 % N/A N/A Bank 1,864,240 13.61 1,438,385 10.50 $ 1,369,891 10.00 % Tier 1 capital to risk weighted assets: Consolidated 1,471,841 10.74 1,164,855 8.50 N/A N/A Bank 1,776,420 12.97 1,164,407 8.50 1,095,913 8.00 Common equity tier 1 to risk weighted assets: Consolidated 1,416,241 10.33 959,293 7.00 N/A N/A Bank 1,776,420 12.97 958,924 7.00 890,429 6.50 Tier 1 capital to average assets: Consolidated 1,471,841 9.12 645,730 4.00 N/A N/A Bank 1,776,420 11.01 645,539 4.00 806,924 5.00 Stock repurchase program: From time to time, the Company's board of directors has authorized stock repurchase programs which allow the Company to purchase its common stock generally over a one-year period at various prices in the open market or in privately negotiated transactions. On October 22, 2020, the Company's board of directors authorized a $150,000 stock repurchase program allowing the Company to purchase shares of its common stock through October 31, 2021. Under this program, the Company repurchased 109,548 shares at a total cost of $5,660 in 2020. There were no shares repurchased under this plan for the three months ended March 31, 2021, or for the three months ended March 31, 2020 under a prior plan. In July 2019, the federal bank regulators adopted final rules that, among other things, eliminated the standalone prior approval requirement for any repurchase of common stock. However, the Company remains subject to a Federal Reserve Board guideline that requires consultation with the Federal Reserve regarding plans for share repurchases on a quarterly basis. The Company’s repurchases of its common stock may be subject to a prior approval or notice requirement under other regulations, policies or supervisory expectations of the Federal Reserve Board. Any redemption or repurchase of preferred stock or subordinated debt remains subject to the prior approval of the Federal Reserve Board.

Subsequent Event

Subsequent Event	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event Declaration of Dividends On April 22, 2021, the Company declared a quarterly cash dividend in the amount of $0.32 per share of common stock to the stockholders of record on May 6, 2021. The dividend will be paid on May 20, 2021.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation: The accompanying consolidated financial statements include the accounts of IBG and all other entities in which IBG has controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. In addition, the Company wholly-owns nine statutory business trusts that were formed for the purpose of issuing trust preferred securities and do not meet the criteria for consolidation. The consolidated interim financial statements are unaudited, but include all adjustments, which, in the opinion of management, are necessary for a fair presentation of the results of the periods presented. All such adjustments were of a normal and recurring nature. These financial statements should be read in conjunction with the financial statements and the notes thereto in the Company's Annual Report on Form 10-K for the year ended December 31, 2020. The consolidated balance sheet at December 31, 2020 has been derived from the audited financial statements as of that date, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. Accounting standards codification: The Financial Accounting Standards Board's (FASB) Accounting Standards Codification (ASC) is the officially recognized source of authoritative U.S. generally accepted accounting principles (GAAP) applicable to all public and non-public non-governmental entities. Rules and interpretive releases of the SEC under the authority of federal securities laws are also sources of authoritative GAAP for SEC registrants. All other accounting literature is considered non-authoritative. Citing particular content in the ASC involves specifying the unique numeric path to the content through the Topic, Subtopic, Section and Paragraph structure.
Segment reporting	Segment reporting: The Company has one reportable segment. The Company’s chief operating decision-maker uses consolidated results to make operating and strategic decisions.
Reclassifications	Reclassifications: Certain prior period financial statement and disclosure amounts have been reclassified to conform to current period presentation. The reclassifications have no effect on net income or stockholders' equity as previously reported.
Use of estimates	Use of estimates: The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Accordingly, actual results could differ from those estimates. The material estimates included in the financial statements relate to the allowance for credit losses, the valuation of goodwill and valuation of assets and liabilities acquired in business combinations.
New accounting standard	Accounting changes: On January 1, 2020, ASU 2016-13, Financial Instruments - Credit Losses (Topic 326) (ASC 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13) , as amended, became effective for the Company. ASU 2016-13 replaces the incurred loss methodology with an expected loss methodology that is referred to as the current expected credit loss (CECL) methodology. The measurement of expected credit losses under the CECL methodology is applicable to financial assets measured at amortized cost, including loan receivables and held-to-maturity debt securities. It also applies to off-balance-sheet credit exposures not accounted for as insurance (loan commitments, standby letters of credit, financial guarantees, and other similar instruments). The CECL model requires the measurement of all expected credit losses on applicable financial assets based on historical experience, current conditions, and reasonable and supportable forecasts. In addition, ASU 2016-13 includes certain changes to the accounting for available-for-sale securities such as requiring credit-related impairments to be recognized as an allowance for credit losses rather than as a direct write-down of the securities amortized cost basis when management does not intend to sell or believes that it is more likely than not they will be required to sell securities prior to recovery of the securities amortized cost basis. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) was signed by the President of the United States that included an option for financial institutions to delay the implementation of ASU 2016-13 until the earlier of the termination date of the national emergency declaration by the President or December 31, 2020. On December 27, 2020, the Consolidated Appropriations Act, 2021 (Act 2021), was signed into law which further extended the implementation date of CECL to the earlier of the first day of the entity’s fiscal year that begins after the date on which the COVID-19 national emergency terminates or January 1, 2022. Under this option, the Company elected to delay implementation of ASU 2016-13 and calculated and recorded its provision for loan losses under the incurred loss model that existed prior to ASU 2016-13 for the year ended December 31, 2020. With regard to Act 2021 amendments, the SEC staff indicated it would not object to a registrant early adopting on December 31, 2020, retrospective to January 1, 2020, or January 1, 2021, effective as of January 1, 2021. Under this guidance, the Company elected to adopt ASU 2016-13 with an effective implementation date of January 1, 2021. The Company adopted ASU 2016-13 using the modified retrospective method for all financial assets measured at amortized cost and off-balance sheet credit exposures. As a result of this adoption, the Company recognized a cumulative effect reduction to retained earnings totaling $53,880, net of a recorded deferred tax asset of $15,113, and reclassed $13,035 of allowance for credit loss related to financial assets purchased with credit deterioration (PCD) that were previously classified as purchased credit impaired (PCI) and accounted for under ASC 310-30 as discussed below. Results for periods beginning after January 1, 2021 are presented in accordance with ASU 2016-13 while prior period amounts continue to be reported in accordance with previously applicable GAAP. The Company adopted ASU 2016-13 using the prospective transition approach for PCD assets. In accordance with the standard, management did not reassess whether PCI assets met the criteria of PCD assets as of the date of adoption. On January 1, 2021, the amortized cost basis of the PCD assets were adjusted to reflect the addition of the allowance for credit losses. The remaining noncredit discount (based on the adjusted amortized cost basis) will be accreted into interest income at the effective interest rate as of January 1, 2021. The following table illustrates the impact of ASU 2016-13 on the allowances for credit losses as of January 1, 2021, the date of adoption: January 1, 2021 Pre-Adoption Allowance Impact of Adoption Post-Adoption Allowance Assets: Allowance for credit losses on Loans: Commercial $ 27,311 $ 17,103 $ 44,414 Commercial real estate, construction, land and land development 50,123 59,683 109,806 Residential real estate 6,786 (2,115) 4,671 Single-family interim construction 2,156 7,179 9,335 Agricultural 337 (178) 159 Consumer 442 (110) 332 Other 242 (224) 18 Unallocated 423 (423) — $ 87,820 $ 80,915 $ 168,735 Liabilities: Allowance for credit losses on off-balance-sheet credit exposures $ — $ 1,113 $ 1,113 In connection with the adoption of ASC 326, the Company revised certain accounting policies and implemented certain accounting policy elections. The revised accounting policies are described below.
Securities	Securities: Securities classified as available for sale are those debt securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity. Any decision to sell a security classified as available for sale would be based on various factors, including significant movements in interest rates, changes in the maturity mix of the Company's assets and liabilities, liquidity needs, regulatory capital considerations and other similar factors. Securities available for sale are reported at fair value with unrealized gains or losses reported as a separate component of other comprehensive income, net of tax. The amortization of premiums and accretion of discounts, computed by the interest method generally over their contractual lives, are recognized in interest income. Premiums on callable securities are amortized to their earliest call date. Realized gains or losses, determined on the basis of the cost of specific securities sold, are included in earnings on the trade date.
Allowance for Credit Losses	Allowance for credit losses - available-for-sale securities: For available-for-sale securities in an unrealized loss position, the Company first assesses whether it intends to sell or it is more-likely-than-not that we will be required to sell the securities before recovery of the amortized cost basis. If either of these criteria is met, the securities amortized cost basis is written down to fair value as a current period expense. If either of the above criteria is not met, the Company evaluates whether the decline in fair value is the result of credit losses or other factors. In making this assessment, management may consider various factors including the extent to which fair value is less than amortized cost, performance of any underlying collateral and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected are compared to the amortized cost basis of the security and any excess of the amortized cost basis over the present value of expected cash flows is recorded as an allowance for credit loss, limited to the amount by which the fair value is less than the amortized cost basis. Any impairment not recorded through an allowance for credit loss is recognized in other comprehensive income as a non credit-related impairment. Management continually evaluates the allowance for credit losses based upon the factors noted above. Should any of the factors considered by management change, the Company’s estimate of credit losses could also change and would affect the level of future provision for credit losses. Portions of the allowance may be allocated for specific credits; however, the entire allowance is available for any credit that, in management’s judgment, should be charged off. While the calculation of the allowance for credit losses utilizes management’s best judgment and all the information available, the adequacy of the allowance for credit losses is dependent on a variety of factors beyond the Company’s control, including, among other things, the performance of the entire loan portfolio, the economy, changes in interest rates and the view of regulatory authorities towards loan classifications. The allowance for credit losses is measured on a collective basis for portfolios of loans when similar risk characteristics exist. Loans that do not share risk characteristics are evaluated for expected credit losses on an individual basis and excluded from the
Acquired Loans	Acquired loans: Loans acquired in connection with a business combination are recorded at their acquisition-date fair value. The allowance for credit losses related to the acquired loan portfolio is not carried over. Acquired loans are classified into two categories based on the credit risk characteristics of the underlying borrowers as either purchased credit deteriorated (PCD) loans, or loans with no evidence of credit deterioration (non-PCD). PCD loans are defined as a loan or pool of loans that have experienced more-than-insignificant credit deterioration since the origination date. For PCD loans, an initial allowance is established on the acquisition date using the same methodology as other loans held for investment and combined with the fair value of the loan to arrive at acquisition date amortized cost. Accordingly, no provision for credit losses is recognized on PCD loans at the acquisition date. Subsequent to the acquisition date, changes to the allowance are recognized in the provision for credit losses. Non-PCD loans are pooled into segments together with originated held for investment loans that share similar risk characteristics and have an allowance established on the acquisition date, which is recognized in the current period provision for credit losses. Determining the fair value of the acquired loans involves estimating the principal and interest payment cash flows expected to be collected on the loans and discounting those cash flows at a market rate of interest. For PCD loans, the non-credit discount or premium is allocated to individual loans as determined by the difference between the loan’s unpaid principal balance and amortized cost basis. The non-credit premium or discount is recognized into interest income on a level yield basis over the remaining expected life of the loan. For non-PCD loans, the fair value discount or premium is allocated to individual loans and recognized into interest income on a level yield basis over the remaining expected life of the loan. Prior to January 1, 2021, loans acquired in a business combination that had evidence of credit impairment and for which it was probable, at acquisition, that the Company would be unable to collect all contractually required payments receivable were considered PCI. PCI loans were accounted for individually or aggregated into pools of loans based on common risk characteristics such as credit grade, loan type, and date of origination.
Loans, Net	Loans, net: Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off are reported at their outstanding principal balance, net of unearned interest, purchase premiums and discounts, deferred loan fees or costs and an allowance for credit losses. Loan origination fees, net of direct origination costs, are deferred and recognized as an adjustment to the related loan yield using the effective interest method without anticipating prepayments. Further information regarding the Company's accounting policies related to past due loans, non-accrual loans, collateral dependent loans and troubled debt restructurings is presented in Note 4 - Loans , N et and Allowance for Credit Losses on Loans .
Allowance for Credit Losses on Loans	Allowance for credit losses on loans: In accordance with ASC 326, the allowance for credit losses on loans is a valuation account that is deducted from the amortized cost basis of loans to present management's best estimate of the net amount expected to be collected on the loans. Loans are charged against the allowance for credit losses when management believes that collectability of the principal is unlikely. Subsequent recoveries, if any, are credited to the allowance. The allowance is increased by provisions reported in the income statement as a component of provision for credit losses. Management has made the accounting policy election to exclude accrued interest receivable on loans from the estimate of credit losses and reports accrued interest separately in other assets in the consolidated balance sheets. Further information regarding Company policies and methodology used to estimate the allowance for credit losses on loans is presented in Note 4 - Loans, Net and Allowance for Credit Losses on Loans .
Allowance For Credit Losses on Off-Balance-Sheet Credit Exposures	Allowance for credit losses on off-balance-sheet credit exposures: The allowance for credit losses on off-balance-sheet credit exposures is a liability account, calculated in accordance with ASC 326, representing expected credit losses over the contractual period for which the Company is exposed to credit risk resulting from a contractual obligation to extend credit. No allowance is recognized if we have the unconditional right to cancel the obligation. The allowance is reported as a component of other liabilities in the consolidated balance sheets. Adjustments to the allowance are reported in the income statement as a component of provision for credit losses. Further information regarding Company policies and methodology used to estimate the allowance for credit losses on off-balance-sheet credit exposures is presented in Note 5 - Off-Balance Sheet Arrangements, Commitments and Contingencies .
Subsequent events	Subsequent events: Companies are required to evaluate events and transactions that occur after the balance sheet date but before the date the financial statements are issued. They must recognize in the financial statements the effect of all events or transactions that provide additional evidence of conditions that existed at the balance sheet date, including the estimates inherent in the financial statement preparation process. Entities shall not recognize the impact of events or transactions that provide evidence about conditions that did not exist at the balance sheet date but arose after that date. The Company has evaluated subsequent events through the date of filing these financial statements with the Securities and Exchange Commission (SEC) and noted no subsequent events requiring financial statement recognition or disclosure, except as disclosed in Note 11.
Earnings per share	Earnings per share: Basic earnings per common share is calculated as net income available to common shareholders divided by the weighted average number of common shares outstanding during the period. The unvested share-based payment awards that contain rights to nonforfeitable dividends are considered participating securities for this calculation. Diluted earnings per common share include the dilutive effect of additional potential common shares issuable under participating nonvested restricted stock awards as well as performance stock units (PSUs). The participating nonvested common stock was not included in dilutive shares as it was anti-dilutive for the three months ended March 31, 2021. Proceeds from the assumed exercise of dilutive participating nonvested restricted stock awards and PSUs are assumed to be used to repurchase common stock at the average market price.
Loan charge-off amounts	The Company will charge-off that portion of any loan which management considers a loss. Commercial and real estate loans are generally considered for charge-off when exposure beyond collateral coverage is apparent and when no further collection of the loss portion is anticipated based on the borrower’s financial condition.
Nonaccrual loan and lease status	The accrual of interest is discontinued on a loan when management believes that, after considering collection efforts and other factors, the borrower's financial condition is such that collection of interest is doubtful, as well as when required by regulatory provisions. Regulatory provisions would typically require the placement of a loan on non-accrual status if 1) principal or interest has been in default for a period of 90 days or more unless the loan is both well secured and in the process of collection or 2) full payment of principal and interest is not expected. All interest accrued but not collected for loans that are placed on nonaccrual status or charged-off is reversed against interest income. Cash collections on nonaccrual loans are generally credited to the loan receivable balance, and no interest income is recognized on those loans until the principal balance has been collected. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured.
Troubled debt restructuring	The restructuring of a loan is considered a “troubled debt restructuring” (TDR) if both 1) the borrower is experiencing financial difficulties and 2) the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, principal forgiveness, extending amortization and other actions intended to minimize potential losses. M
Loans past due	Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due.
Fair value measurements	The fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. ASC Topic 820, Fair Value Measurements and Disclosures , establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: Level 1 Inputs – Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 Inputs – Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. Level 3 Inputs – Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. The Company elected the fair value option for certain residential mortgage loans held for sale in accordance with ASC 825, Financial Instruments. This election allows for a more effective offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . The Company has not elected the fair value option for other residential mortgage loans held for sale primarily because they are not economically hedged using derivative instruments. See below and Note 8, Derivative Financial Instruments , for additional information. Investment securities Securities classified as available for sale are reported at fair value utilizing Level 1 and Level 2 inputs. Securities are classified within Level 1 when quoted market prices are available in an active market. Inputs include securities that have quoted prices in active markets for identical assets. For securities utilizing Level 2 inputs, the Company obtains fair value measurements from an independent pricing service. The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury and other yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Loans held for sale Certain mortgage loans held for sale are measured at fair value on a recurring basis due to the Company's election to adopt fair value accounting treatment for those loans originated for which the Company has entered into certain derivative financial instruments as part of its mortgage banking and related risk management activities. These instruments include interest rate lock commitments and mandatory forward commitments to sell these loans to investors known as forward mortgage-backed securities trades. This election allows for a more effective offset of the changes in fair values of the assets and the mortgage related derivative instruments used to economically hedge them without the burden of complying with the requirements for hedge accounting under ASC 815, Derivatives and Hedging . Mortgage loans held for sale, for which the fair value option was elected, which are sold on a servicing released basis, are valued using a market approach by utilizing either: (i) the fair value of securities backed by similar mortgage loans, adjusted for certain factors to approximate the fair value of a whole mortgage loan, including the value attributable to mortgage servicing and credit risk, (ii) current commitments to purchase loans or (iii) recent observable market trades for similar loans, adjusted to credit risk and other individual loan characteristics. As these prices are derived from market observable inputs, the Company classifies these valuations as Level 2 in the fair value disclosures. For mortgage loans held for sale for which the fair value option was elected, the earned current contractual interest payment is recognized in interest income, loan origination costs and fees on fair value option loans are recognized in earnings as incurred and not deferred. The Company has no continuing involvement in any residential mortgage loans sold. Derivatives The estimated fair values of interest rate lock commitments utilize current secondary market prices for underlying loans and estimated servicing value with similar coupons, maturity and credit quality, subject to the anticipated loan funding probability (pull-through rate). The fair value of interest rate lock commitments is subject to change primarily due to changes in interest rates and the estimated pull-through rate. These commitments are classified as Level 2 in the fair value disclosures, as the valuations are based on observable market inputs. Forward mortgage-backed securities trades are exchange-traded or traded within highly active dealer markets. In order to determine the fair value of these instruments, the Company utilized the exchange price or dealer market price for the particular derivative contract; therefore these contracts are classified as Level 2. The estimated fair values are subject to change primarily due to changes in interest rates. The Company also enters into certain interest rate derivative positions that are not designated as hedging instruments. The estimated fair value of these commercial loan interest rate swaps are obtained from a pricing service that provides the swaps' unwind value (Level 2 inputs). See Note 8, Derivative Financial Instruments , for more information. Individually evaluated loans (loans which are not expected to repay all principal and interest amounts due in accordance with the original contractual terms) are measured at an observable market price (if available) or at the fair value of the loan’s collateral (if collateral dependent). Fair value of the loan’s collateral is determined by appraisals or independent valuation, which is then adjusted for the estimated costs related to liquidation of the collateral. Management’s ongoing review of appraisal information may result in additional discounts or adjustments to valuation based upon more recent market sales activity or more current appraisal information derived from properties of similar type and/or locale. In addition, management's discounting criteria may vary for loans secured by non-real estate collateral such as inventory, oil and gas reserves, accounts receivable, equipment or other business assets. Therefore, the Company has categorized its individually evaluated loans as Level 3. Other real estate is measured at fair value on a nonrecurring basis (upon initial recognition or subsequent impairment). Other real estate is classified within Level 3 of the valuation hierarchy. When transferred from the loan portfolio, other real estate is adjusted to fair value less estimated selling costs and is subsequently carried at the lower of carrying value or fair value less estimated selling costs. The fair value is determined using an external appraisal process, discounted based on internal criteria. Therefore, the Company has categorized its other real estate as Level 3. There was no other real estate owned remeasured during the three months ended March 31, 2021 and the year ended December 31, 2020. The methods and assumptions used by the Company in estimating fair values of financial instruments as disclosed herein in accordance with ASC Topic 825, Financial Instruments , other than for those measured at fair value on a recurring and nonrecurring basis discussed above, are as follows: Cash and cash equivalents: The carrying amounts of cash and cash equivalents approximate their fair value. Certificates of deposit held in other banks: The fair value of certificates of deposit held in other banks is based upon current market rates. Loans held for sale, at cost: The fair value of loans held for sale is determined based upon commitments on hand from investors. Loans: A discounted cash flow model is used to estimate the fair value of the loans. The discounted cash flow approach models the credit losses directly in the projected cash flows, applying various assumptions regarding credit, interest and prepayment risks for the loans based on loan types, payment types and fixed or variable classifications. Federal Home Loan Bank of Dallas and other restricted stock: The carrying value of restricted securities such as stock in the Federal Home Loan Bank of Dallas and Independent Bankers Financial Corporation approximates fair value. Deposits: The fair values disclosed for demand deposits are, by definition, equal to the amount payable on demand at the reporting date (that is their carrying amounts). The carrying amounts of variable-rate certificates of deposit (CDs) approximate their fair values at the reporting date. Fair values for fixed-rate CDs are estimated using a discounted cash flow calculation that applies interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities on time deposits. Federal Home Loan Bank advances, line of credit and federal funds purchased: The fair value of advances maturing within 90 days approximates carrying value. Fair value of other advances is based on the Company’s current borrowing rate for similar arrangements. Other borrowings: The estimated fair value approximates carrying value for short-term borrowings. The fair value of private subordinated debentures are based upon prevailing rates on similar debt in the market place. The subordinated debentures that are publicly traded are valued based on indicative bid prices based upon market pricing observations in the current market. Junior subordinated debentures: The fair value of junior subordinated debentures is estimated using discounted cash flow analyses based on the published Bloomberg US Financials BB rated corporate bond index yield. Accrued interest: The carrying amounts of accrued interest approximate their fair values. Off-balance sheet instruments: Fair values for off-balance sheet, credit-related financial instruments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the counterparties' credit standing. The fair value of commitments is not material.
Derivatives	The Company enters into certain derivative financial instruments as part of its hedging strategy. These financial instruments are not designated as hedging instruments and are used for asset and liability management related to the Company's mortgage banking activities and commercial customers' financing needs. All derivatives are carried at fair value in either other assets or other liabilities. Through the normal course of business, the Company enters into interest rate lock commitments with consumers to originate mortgage loans at a specified interest rate. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by the Company. The Company manages the changes in fair value associated with changes in interest rates related to interest rate lock commitments by using forward sold commitments known as forward mortgage-backed securities trades. These instruments are typically entered into at the time the interest rate lock commitment is made.
Share repurchase program	Stock repurchase program: From time to time, the Company's board of directors has authorized stock repurchase programs which allow the Company to purchase its common stock generally over a one-year period at various prices in the open market or in privately negotiated transactions. On October 22, 2020, the Company's board of directors authorized a $150,000 stock repurchase program allowing the Company to purchase shares of its common stock through October 31, 2021. Under this program, the Company repurchased 109,548 shares at a total cost of $5,660 in 2020. There were no shares repurchased under this plan for the three months ended March 31, 2021, or for the three months ended March 31, 2020 under a prior plan. In July 2019, the federal bank regulators adopted final rules that, among other things, eliminated the standalone prior approval requirement for any repurchase of common stock. However, the Company remains subject to a Federal Reserve Board guideline that requires consultation with the Federal Reserve regarding plans for share repurchases on a quarterly basis. The Company’s repurchases of its common stock may be subject to a prior approval or notice requirement under other regulations, policies or supervisory expectations of the Federal Reserve Board. Any redemption or repurchase of preferred stock or subordinated debt remains subject to the prior approval of the Federal Reserve Board.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	Jan. 01, 2021	Mar. 31, 2021
Accounting Policies [Abstract]
Accounting Standards Update and Change in Accounting Principle	The following table illustrates the impact of ASU 2016-13 on the allowances for credit losses as of January 1, 2021, the date of adoption: January 1, 2021 Pre-Adoption Allowance Impact of Adoption Post-Adoption Allowance Assets: Allowance for credit losses on Loans: Commercial $ 27,311 $ 17,103 $ 44,414 Commercial real estate, construction, land and land development 50,123 59,683 109,806 Residential real estate 6,786 (2,115) 4,671 Single-family interim construction 2,156 7,179 9,335 Agricultural 337 (178) 159 Consumer 442 (110) 332 Other 242 (224) 18 Unallocated 423 (423) — $ 87,820 $ 80,915 $ 168,735 Liabilities: Allowance for credit losses on off-balance-sheet credit exposures $ — $ 1,113 $ 1,113
Earning Per Share		The following table presents a reconciliation of net income available to common shareholders and the number of shares used in the calculation of basic and diluted earnings per common share. Three Months Ended March 31, 2021 2020 Basic earnings per share: Net income $ 59,980 $ 44,167 Less: Undistributed earnings allocated to participating securities 487 209 Dividends paid on participating securities 134 68 Net income available to common shareholders $ 59,359 $ 43,890 Weighted average basic shares outstanding 42,731,456 42,741,399 Basic earnings per share $ 1.39 $ 1.03 Diluted earnings per share: Net income available to common shareholders $ 59,359 $ 43,890 Total weighted average basic shares outstanding 42,731,456 42,741,399 Add dilutive performance stock units 44,321 — Add dilutive participating securities — 8,559 Total weighted average diluted shares outstanding 42,775,777 42,749,958 Diluted earnings per share $ 1.39 $ 1.03 Anti-dilutive participating securities 202,811 —

Statement of Cash Flows (Tables

Statement of Cash Flows (Tables)	3 Months Ended
	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Other Supplemental Cash Flow Information	Other supplemental cash flow information is presented below: Three Months Ended March 31, 2021 2020 Cash transactions: Interest expense paid $ 21,785 $ 35,400 Income taxes paid $ 8 $ — Noncash transactions: Deferred dividend equivalents $ 82 $ — Transfers of loans to other real estate owned $ — $ 3,914 Loans to facilitate the sale of other real estate owned $ — $ 1,564 Securities purchased, not yet settled $ 5,000 $ — Right-of-use assets obtained in exchange for lease liabilities $ 57 $ — Transfer of premises and equipment to other assets $ 88 $ —

Securities Available for Sale (

Securities Available for Sale (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Securities, Available-for-sale [Abstract]
Amortized Cost of Securities and Approximate Fair Values	The amortized cost of securities and their approximate fair values at March 31, 2021 and December 31, 2020 are as follows: Amortized Cost (1) Gross Gross Fair Securities Available for Sale March 31, 2021 U.S. treasuries $ 33,051 $ 1,401 $ — $ 34,452 Government agency securities 295,580 2,806 (8,746) 289,640 Obligations of state and municipal subdivisions 373,045 16,044 (1,233) 387,856 Corporate bonds 28,494 580 (79) 28,995 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 552,910 17,777 (4,873) 565,814 Other securities 1,200 — — 1,200 $ 1,284,280 $ 38,608 $ (14,931) $ 1,307,957 December 31, 2020 U.S. treasuries $ 43,060 $ 1,648 $ — $ 44,708 Government agency securities 247,764 3,169 (1,916) 249,017 Obligations of state and municipal subdivisions 373,017 20,168 (20) 393,165 Corporate bonds 21,496 608 (2) 22,102 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 421,916 21,678 (93) 443,501 Other securities 1,200 — — 1,200 $ 1,108,453 $ 47,271 $ (2,031) $ 1,153,693
Proceeds from Sale of Available for Sale Securities	Proceeds from sale of securities available for sale and gross gains and gross losses for the three months ended March 31, 2021 and 2020 were as follows: Three Months Ended March 31, 2021 2020 Proceeds from sale $ — $ 13,100 Gross gains $ — $ 359 Gross losses $ — $ 3
Amortized Cost and Estimated Fair Value of Securities Available for Sale by Contractual Maturity	The amortized cost and estimated fair value of securities available for sale at March 31, 2021, by contractual maturity, are shown below. Maturities of mortgage-backed securities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. March 31, 2021 Securities Available for Sale Amortized Cost (1) Fair Value Due in one year or less $ 27,652 $ 27,986 Due from one year to five years 137,914 143,780 Due from five to ten years 247,804 249,486 Thereafter 318,000 320,891 731,370 742,143 Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 552,910 565,814 $ 1,284,280 $ 1,307,957
Summary of Unrealized Losses and Fair Value Securities in Continuous Unrealized Loss Position	The number of securities, unrealized losses and fair value, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, as of March 31, 2021 and December 31, 2020, are summarized as follows: Less Than 12 Months Greater Than 12 Months Total Description of Securities Number of Securities Estimated Unrealized Number of Securities Estimated Unrealized Estimated Unrealized Securities Available for Sale March 31, 2021 Government agency securities 31 $ 181,215 $ (8,746) — $ — $ — $ 181,215 $ (8,746) Obligations of state and municipal subdivisions 12 46,956 (1,233) — — — 46,956 (1,233) Corporate bonds 3 5,421 (79) — — — 5,421 (79) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 33 188,714 (4,873) — — — 188,714 (4,873) 79 $ 422,306 $ (14,931) — $ — $ — $ 422,306 $ (14,931) December 31, 2020 Government agency securities 20 112,897 (1,916) — — — 112,897 (1,916) Obligations of state and municipal subdivisions 2 3,786 (20) — — — 3,786 (20) Corporate bonds 1 998 (2) — — — 998 (2) Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 10 41,344 (93) — — — 41,344 (93) 33 $ 159,025 $ (2,031) — $ — $ — $ 159,025 $ (2,031)

Loans, Net and Allowance for _2

Loans, Net and Allowance for Credit Losses on Loans (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Compositions of Loans	Loans, net, at March 31, 2021 and December 31, 2020, consisted of the following: March 31, December 31, 2021 2020 Commercial $ 3,596,654 $ 3,902,266 Real estate: Commercial 6,194,353 6,096,676 Commercial construction, land and land development 1,206,350 1,245,801 Residential 1,310,371 1,352,465 Single-family interim construction 312,975 326,575 Agricultural 74,820 85,014 Consumer 74,923 66,952 Other 311 346 Total loans (1)(2) 12,770,757 13,076,095 Deferred loan fees, net (1) — (10,037) Allowance for credit losses (165,827) (87,820) Total loans, net (2) $ 12,604,930 $ 12,978,238
Summary of Activity in Allowance for Credit Losses by Loan Class	The following is a summary of the activity in the allowance for credit losses on loans by class for the three months ended March 31, 2021 and 2020: Commercial Commercial Residential Single-Family Agricultural Consumer Other Unallocated Total Three months ended March 31, 2021 Balance at beginning of period $ 27,311 $ 50,123 $ 6,786 $ 2,156 $ 337 $ 442 $ 242 $ 423 $ 87,820 Impact of adopting ASC 326 12,775 51,116 (2,255) 7,179 (178) (110) (224) (423) 67,880 Initial allowance on loans purchased with credit deterioration 4,328 8,567 140 — — — — — 13,035 Provision for credit losses 4,501 (5,932) (270) (1,007) (51) 36 223 — (2,500) Charge-offs (70) (301) — — — (18) (57) — (446) Recoveries 18 — — — — 3 17 — 38 Balance at end of period $ 48,863 $ 103,573 $ 4,401 $ 8,328 $ 108 $ 353 $ 201 $ — $ 165,827 Three months ended March 31, 2020 Balance at beginning of period $ 12,844 $ 33,085 $ 3,678 $ 1,606 $ 332 $ 226 $ 5 $ (315) $ 51,461 Provision for credit losses 5,053 1,733 759 307 13 28 131 357 8,381 Charge-offs (571) (735) — (82) — (9) (112) — (1,509) Recoveries 16 — — — — 18 36 — 70 Balance at end of period $ 17,342 $ 34,083 $ 4,437 $ 1,831 $ 345 $ 263 $ 60 $ 42 $ 58,403
Individually Evaluated Loans	The following table presents loans that were evaluated for expected credit losses on an individual basis and the related specific credit loss allocations, by loan class as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Loan Balance - Specific Allocations Loan Balance - Specific Allocations Commercial $ 44,933 $ 15,948 $ 39,298 $ 8,281 Commercial real estate, construction, land and land development 27,211 3,863 21,880 243 Residential real estate — — 2,550 — Single-family Interim construction — — — — Agricultural — — 613 — Consumer — — 42 — Other — — — — $ 72,144 $ 19,811 $ 64,383 $ 8,524
Summary of Nonperforming Loans by Loan Class	Nonperforming loans by loan class at March 31, 2021 (at amortized cost) and December 31, 2020 (at recorded investment), are summarized as follows: Commercial Commercial Residential Real Estate Single-Family Agricultural Consumer Other Total March 31, 2021 Nonaccrual loans (1) $ 32,912 $ 22,312 $ 2,289 $ — $ 551 $ 26 $ — $ 58,090 Loans past due 90 days and still accruing 316 — — — — — — 316 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) — 1,786 173 — — — — 1,959 $ 33,228 $ 24,098 $ 2,462 $ — $ 551 $ 26 $ — $ 60,365 December 31, 2020 (2) Nonaccrual loans $ 25,898 $ 20,072 $ 2,372 $ — $ 613 $ 42 $ — $ 48,997 Loans past due 90 days and still accruing 433 — — — — — — 433 Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing) — 1,808 178 — — — — 1,986 $ 26,331 $ 21,880 $ 2,550 $ — $ 613 $ 42 $ — $ 51,416 ____________ (1) There are $3,016 in loans on nonaccrual without an allowance for credit loss as of March 31, 2021. Additionally, no interest income was recognized on nonaccrual loans. No significant amounts of accrued interest was reversed during the three months ended March 31, 2021. (2) Excluded loans acquired with deteriorated credit quality under prior GAAP.
Summary of Troubled Debt Restructurings	Following is a summary of loans modified under troubled debt restructurings during the three months ended March 31, 2021 and 2020: Commercial Commercial Residential Single-Family Agricultural Consumer Other Total Troubled debt restructurings during the three months ended March 31, 2021 Number of contracts 1 — — — — — — 1 Pre-restructuring outstanding recorded investment $ 49 $ — $ — $ — $ — $ — $ — $ 49 Post-restructuring outstanding recorded investment $ 44 $ — $ — $ — $ — $ — $ — $ 44 Troubled debt restructurings during the three months ended March 31, 2020 Number of contracts — 1 — — — — — 1 Pre-restructuring outstanding recorded investment $ — $ 1,517 $ — $ — $ — $ — $ — $ 1,517 Post-restructuring outstanding recorded investment $ — $ 1,517 $ — $ — $ — $ — $ — $ 1,517
Aging of Past Due Loans by Loan Class	The following table presents information regarding the aging of past due loans by loan class as of March 31, 2021 (at amortized cost) and as of December 31, 2020 (at recorded investment): Loans Loans Total Past Current Total March 31, 2021 Commercial $ 1,185 $ 20,422 $ 21,607 $ 3,575,047 $ 3,596,654 Commercial real estate, construction, land and land development 6,223 15,844 22,067 7,378,636 7,400,703 Residential real estate 3,175 1,357 4,532 1,305,839 1,310,371 Single-family interim construction 355 — 355 312,620 312,975 Agricultural 37 — 37 74,783 74,820 Consumer 91 21 112 74,811 74,923 Other — — — 311 311 $ 11,066 $ 37,644 $ 48,710 $ 12,722,047 $ 12,770,757 December 31, 2020 (1) Commercial $ 3,243 $ 13,227 $ 16,470 $ 3,846,810 $ 3,863,280 Commercial real estate, construction, land and land development 2,453 16,790 19,243 7,152,247 7,171,490 Residential real estate 5,169 1,028 6,197 1,341,587 1,347,784 Single-family interim construction — — — 326,575 326,575 Agricultural — 1 1 84,896 84,897 Consumer 86 41 127 66,810 66,937 Other — — — 346 346 10,951 31,087 42,038 12,819,271 12,861,309 Acquired with deteriorated credit quality 624 3,219 3,843 210,943 214,786 $ 11,575 $ 34,306 $ 45,881 $ 13,030,214 $ 13,076,095
Summary of Loans by Credit Quality Indicator by Class	The following summarizes the amortized cost basis of loans by year of origination/renewal and credit quality indicator by class of loan as of March 31, 2021: Revolving Loans Converted to Term Loans Term Loans by Year of Origination Revolving Loans March 31, 2021 2021 2020 2019 2018 2017 Prior Total Commercial Pass $ 282,123 $ 937,698 $ 159,944 $ 138,458 $ 128,778 $ 156,849 $ 1,571,377 $ 3,269 $ 3,378,496 Pass/Watch 472 1,922 1,650 10,446 9,389 99 44,719 1,336 70,033 Special Mention — 3,938 19,103 7,959 443 1,020 3,023 — 35,486 Substandard 13,148 851 33,434 8,178 9,262 17,383 18,474 — 100,730 Doubtful — — 1,745 — — — 10,164 — 11,909 Total commercial $ 295,743 $ 944,409 $ 215,876 $ 165,041 $ 147,872 $ 175,351 $ 1,647,757 $ 4,605 $ 3,596,654 Commercial real estate Pass $ 396,430 $ 1,440,420 $ 968,483 $ 835,598 $ 746,267 $ 1,005,653 $ 62,697 $ 336 $ 5,455,884 Pass/Watch 47,331 47,901 70,961 81,980 34,548 73,083 1 499 356,304 Special Mention 7,960 54,141 40,520 77,624 52,831 54,845 — — 287,921 Substandard 16,617 37,704 2,418 3,128 1,593 31,210 1,574 — 94,244 Doubtful — — — — — — — — — Total commercial real estate $ 468,338 $ 1,580,166 $ 1,082,382 $ 998,330 $ 835,239 $ 1,164,791 $ 64,272 $ 835 $ 6,194,353 Commercial construction, land and land development Pass $ 151,932 $ 365,287 $ 310,392 $ 177,927 $ 25,629 $ 20,017 $ 9,647 $ — $ 1,060,831 Pass/Watch 1,984 4,659 28,682 18,227 10,397 272 — — 64,221 Special Mention — 16,205 15,981 — 9,999 — — — 42,185 Substandard 11,593 3,990 1,435 20,068 30 1,997 — — 39,113 Doubtful — — — — — — — — — Total commercial construction, land and land development $ 165,509 $ 390,141 $ 356,490 $ 216,222 $ 46,055 $ 22,286 $ 9,647 $ — $ 1,206,350 Residential real estate Pass $ 77,163 $ 343,414 $ 270,486 $ 167,961 $ 127,440 $ 242,257 $ 59,961 $ 1,462 $ 1,290,144 Pass/Watch 649 594 1,419 423 548 5,860 65 — 9,558 Special Mention 1,398 1,154 — 133 260 1,174 230 — 4,349 Substandard 189 648 614 1,013 842 2,957 57 — 6,320 Doubtful — — — — — — — — — Total residential real estate $ 79,399 $ 345,810 $ 272,519 $ 169,530 $ 129,090 $ 252,248 $ 60,313 $ 1,462 $ 1,310,371 Revolving Loans Converted to Term Loans Term Loans by Year of Origination Revolving Loans March 31, 2021 2021 2020 2019 2018 2017 Prior Total Single-family interim construction Pass $ 62,725 $ 209,338 $ 26,092 $ 363 $ — $ 380 $ 13,373 $ — $ 312,271 Pass/Watch — 704 — — — — — — 704 Special Mention — — — — — — — — — Substandard — — — — — — — — — Doubtful — — — — — — — — — Total single-family interim construction $ 62,725 $ 210,042 $ 26,092 $ 363 $ — $ 380 $ 13,373 $ — $ 312,975 Agricultural Pass $ 3,041 $ 21,531 $ 4,899 $ 10,382 $ 14,889 $ 6,620 $ 6,547 $ — $ 67,909 Pass/Watch — 552 1,698 66 — 146 2,509 — 4,971 Special Mention — — — — 1,000 — 336 — 1,336 Substandard 2 — — — — 602 — — 604 Doubtful — — — — — — — — — Total agricultural $ 3,043 $ 22,083 $ 6,597 $ 10,448 $ 15,889 $ 7,368 $ 9,392 $ — $ 74,820 Consumer Pass $ 2,486 $ 13,632 $ 3,893 $ 1,911 $ 758 $ 640 $ 51,464 $ 50 $ 74,834 Pass/Watch — — — — 4 — — — 4 Special Mention — — — — — — — — — Substandard — 32 7 — 13 33 — — 85 Doubtful — — — — — — — — — Total consumer $ 2,486 $ 13,664 $ 3,900 $ 1,911 $ 775 $ 673 $ 51,464 $ 50 $ 74,923 Other Pass $ 311 $ — $ — $ — $ — $ — $ — $ — $ 311 Pass/Watch — — — — — — — — — Special Mention — — — — — — — — — Substandard — — — — — — — — — Doubtful — — — — — — — — — Total other $ 311 $ — $ — $ — $ — $ — $ — $ — $ 311 A summary of loans at recorded investment by credit quality indicator by class presented under prior GAAP as of December 31, 2020, is as follows: Pass Pass/ Special Mention Substandard Doubtful Total December 31, 2020 Commercial $ 3,700,626 $ 55,960 $ 38,186 $ 97,403 $ 10,091 $ 3,902,266 Commercial real estate, construction, land and land development 6,504,933 352,910 360,963 123,671 — 7,342,477 Residential real estate 1,332,757 6,296 5,726 7,686 — 1,352,465 Single-family interim construction 323,800 2,775 — — — 326,575 Agricultural 76,951 6,194 1,205 664 — 85,014 Consumer 66,854 8 — 90 — 66,952 Other 346 — — — — 346 $ 12,006,267 $ 424,143 $ 406,080 $ 229,514 $ 10,091 $ 13,076,095

Off-Balance Sheet Arrangement_2

Off-Balance Sheet Arrangements, Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	At March 31, 2021 and December 31, 2020, the approximate amounts of these financial instruments were as follows: March 31, December 31, 2021 2020 Commitments to extend credit $ 2,338,297 $ 2,268,216 Standby letters of credit 25,849 25,917 $ 2,364,146 $ 2,294,133
Commitments Off Balance Sheet Allowance for Credit Losses	The allowance for credit losses on off-balance-sheet commitments were as follows: Three Months Ended March 31, 2021 2020 Balance at beginning of period $ — $ — Impact of CECL adoption 1,113 — Provision for off-balance sheet credit exposure — — Balance at end of period $ 1,113 $ —

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Income Tax Expense	Income tax expense for the three months ended March 31, 2021 and 2020 was as follows: Three Months Ended March 31, 2021 2020 Income tax expense for the period $ 15,745 $ 10,836 Effective tax rate 20.8 % 19.7 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Assets at Fair Value on Recurring Basis	The following table represents assets and liabilities reported on the consolidated balance sheets at their fair value on a recurring basis as of March 31, 2021 and December 31, 2020 by level within the ASC Topic 820 fair value measurement hierarchy: Fair Value Measurements at Reporting Date Using Assets/ Quoted Prices Significant Significant March 31, 2021 Assets: Investment securities available for sale: U.S. treasuries $ 34,452 $ — $ 34,452 $ — Government agency securities 289,640 — 289,640 — Obligations of state and municipal subdivisions 387,856 — 387,856 — Corporate bonds 28,995 — 28,995 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 565,814 — 565,814 — Other securities 1,200 — 1,200 — Loans held for sale, fair value option elected (1) 53,930 — 53,930 — Derivative financial instruments: Interest rate lock commitments 2,158 — 2,158 — Forward mortgage-backed securities trades 787 — 787 — Loan customer counterparty 12,427 — 12,427 — Financial institution counterparty 1,372 — 1,372 — Liabilities: Derivative financial instruments: Interest rate lock commitments 52 — 52 — Forward mortgage-backed securities trades 9 — 9 — Loan customer counterparty 1,291 — 1,291 — Financial institution counterparty 12,952 — 12,952 — December 31, 2020 Assets: Investment securities available for sale: U.S. treasuries $ 44,708 $ — $ 44,708 $ — Government agency securities 249,017 — 249,017 — Obligations of state and municipal subdivisions 393,165 — 393,165 — Corporate bonds 22,102 — 22,102 — Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA 443,501 — 443,501 — Other securities 1,200 — 1,200 — Loans held for sale, fair value option elected (1) 71,769 — 71,769 — Derivative financial instruments: Interest rate lock commitments 3,515 — 3,515 — Loan customer counterparty 20,159 — 20,159 — Liabilities: Derivative financial instruments: Forward mortgage-backed securities trades 568 — 568 — Financial institution counterparty 21,306 — 21,306 — ____________ (1) At March 31, 2021 and December 31, 2020, loans held for sale for which the fair value option was elected had an aggregate outstanding principal balance of $53,030 and $68,670, respectively. There were no mortgage loans held for sale under the fair value option that were 90 days or greater past due or on nonaccrual at March 31, 2021.
Assets and Liabilities at Fair Value on Nonrecurring Basis	The following table presents the assets carried on the consolidated balance sheet by caption and by level in the fair value hierarchy at March 31, 2021 and December 31, 2020, for which a nonrecurring change in fair value has been recorded: Fair Value Measurements at Reporting Date Using Assets Quoted Prices Significant Significant Period Ended March 31, 2021 Assets: Individually evaluated loans $ 12,481 $ — $ — $ 12,481 $ 2,773 December 31, 2020 Assets: Individually evaluated loans $ 16,903 $ — $ — $ 16,903 $ 13,041
Carrying Amount and Estimated Fair Value of Financial Instruments	The carrying amount, estimated fair value and the level of the fair value hierarchy of the Company’s financial instruments that are reported at amortized cost on the Company's consolidated balance sheets were as follows at March 31, 2021 and December 31, 2020: Fair Value Measurements at Reporting Date Using Carrying Estimated Quoted Prices Significant Significant March 31, 2021 Financial assets: Cash and cash equivalents $ 2,416,870 $ 2,416,870 $ 2,416,870 $ — $ — Certificates of deposit held in other banks 4,482 4,569 — 4,569 — Loans held for sale, at cost 3,869 3,963 — 3,963 — Loans, net 12,604,930 12,809,647 — — 12,809,647 FHLB of Dallas stock and other restricted stock 20,338 20,338 — 20,338 — Accrued interest receivable 59,896 59,896 — 59,896 — Financial liabilities: Deposits 14,803,792 14,810,771 — 14,810,771 — Accrued interest payable 3,654 3,654 — 3,654 — FHLB advances 375,000 366,583 — 366,583 — Other borrowings 308,350 327,350 — 327,350 — Junior subordinated debentures 54,072 41,292 — 41,292 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — — December 31, 2020 Financial assets: Cash and cash equivalents $ 1,813,987 $ 1,813,987 $ 1,813,987 $ — $ — Certificates of deposit held in other banks 4,482 4,595 — 4,595 — Loans held for sale, at cost 10,878 11,138 — 11,138 — Loans, net 12,978,238 13,093,698 — — 13,093,698 FHLB of Dallas stock and other restricted stock 20,305 20,305 — 20,305 — Accrued interest receivable 60,581 60,581 — 60,581 — Financial liabilities: Deposits 14,398,927 14,407,596 — 14,407,596 — Accrued interest payable 7,397 7,397 — 7,397 — FHLB advances 375,000 371,175 — 371,175 — Other borrowings 312,175 327,150 — 327,150 — Junior subordinated debentures 54,023 42,624 — 42,624 — Off-balance sheet assets (liabilities): Commitments to extend credit — — — — — Standby letters of credit — — — — —

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional Balances and Fair Values of Outstanding Positions	The following table provides the outstanding notional balances and fair values of outstanding derivative positions at March 31, 2021 and December 31, 2020: Outstanding Notional Balance Asset Derivative Liability Derivative March 31, 2021 Interest rate lock commitments $ 90,496 $ 2,158 $ 52 Forward mortgage-backed securities trades 80,000 787 9 Commercial loan interest rate swaps: Loan customer counterparty 323,760 12,427 1,291 Financial institution counterparty 323,760 1,372 12,952 December 31, 2020 Interest rate lock commitments $ 116,795 $ 3,515 $ — Forward mortgage-backed securities trades 104,000 — 568 Commercial loan interest rate swaps: Loan customer counterparty 335,370 20,159 — Financial institution counterparty 335,370 — 21,306
Schedule of Weighted Average Interest Rate Received and Paid	The commercial loan customer counterparty weighted average received and paid interest rates for interest rate swaps outstanding were as follows: Weighted Average Interest Rate March 31, 2021 December 31, 2020 Received Paid Received Paid Loan customer counterparty 4.08 % 2.28 % 4.08 % 2.32 %
Income on Derivatives Not Designated as Hedging Instruments	Income (loss) for the three months ended March 31, 2021 and 2020 was as follows: Three Months Ended March 31, 2021 2020 Derivatives not designated as hedging instruments Interest rate lock commitments $ (1,409) $ 551 Forward mortgage-backed securities trades 1,346 (1,252)

Stock Awards (Tables)

Stock Awards (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Nonvested Shares Activity	The following table summarizes the activity in nonvested restricted stock awards for the three months ended March 31, 2021 and 2020: Restricted Stock Awards Number of Weighted Average Nonvested shares, December 31, 2020 468,800 $ 49.01 Granted during the period 83,494 63.36 Vested during the period (106,107) 56.51 Forfeited during the period (4,506) 53.26 Nonvested shares, March 31, 2021 441,681 $ 49.88 Nonvested shares, December 31, 2019 284,861 $ 58.63 Granted during the period 94,177 53.48 Vested during the period (78,599) 57.94 Nonvested shares, March 31, 2020 300,439 $ 57.19
Schedule of Future Vesting of Restricted Stock Award	At March 31, 2021, the future vesting schedule of the nonvested restricted stock awards is as follows: First year 174,575 Second year 131,015 Third year 83,160 Fourth year 52,731 Fifth year 200 Total nonvested shares 441,681
Nonvested performance stock units	The following table summarizes the activity in nonvested performance stock units at target award level for the three months ended March 31, 2021: Performance-based Restricted Stock Units Number of Weighted Average Nonvested shares, December 31, 2020 89,300 $ 38.29 Granted during the period 20,198 62.58 Nonvested shares, March 31, 2021 109,498 $ 42.77

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2021
Regulated Operations [Abstract]
Schedule of Compliance with Regulatory Capital Requirements	The following table presents actual capital amounts and required ratios under Basel III Capital Rules for the Company and Bank as of March 31, 2021 and December 31, 2020. Actual Minimum Capital To Be Well Capitalized Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio March 31, 2021 Total capital to risk weighted assets: Consolidated $ 1,874,814 14.13 % $ 1,393,602 10.50 % N/A N/A Bank 1,904,255 14.35 1,393,159 10.50 $ 1,326,819 10.00 % Tier 1 capital to risk weighted assets: Consolidated 1,507,307 11.36 1,128,154 8.50 N/A N/A Bank 1,802,748 13.59 1,127,796 8.50 1,061,455 8.00 Common equity tier 1 to risk weighted assets: Consolidated 1,451,707 10.94 929,068 7.00 N/A N/A Bank 1,802,748 13.59 928,773 7.00 862,432 6.50 Tier 1 capital to average assets: Consolidated 1,507,307 9.01 668,972 4.00 N/A N/A Bank 1,802,748 10.78 668,786 4.00 835,983 5.00 December 31, 2020 Total capital to risk weighted assets: Consolidated $ 1,825,661 13.32 % $ 1,438,939 10.50 % N/A N/A Bank 1,864,240 13.61 1,438,385 10.50 $ 1,369,891 10.00 % Tier 1 capital to risk weighted assets: Consolidated 1,471,841 10.74 1,164,855 8.50 N/A N/A Bank 1,776,420 12.97 1,164,407 8.50 1,095,913 8.00 Common equity tier 1 to risk weighted assets: Consolidated 1,416,241 10.33 959,293 7.00 N/A N/A Bank 1,776,420 12.97 958,924 7.00 890,429 6.50 Tier 1 capital to average assets: Consolidated 1,471,841 9.12 645,730 4.00 N/A N/A Bank 1,776,420 11.01 645,539 4.00 806,924 5.00

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)segmentbusiness_trust	Jan. 01, 2021USD ($)	Dec. 31, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of wholly owned statutory business trusts | business_trust	9
Number of reportable segments | segment	1
Cumulative effect reduction to retained earnings	$ (2,493,117)		$ (2,515,371)	$ (2,386,285)	$ (2,339,773)
Deferred Tax Assets, Allowance for Credit Losses		$ 15,113
Allowance for loan losses on PCI loans	165,827	87,820	87,820	58,403	51,461
Accounting Standards Update 2016-13 | Acquired with deteriorated credit quality
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan losses on PCI loans		13,035
Cumulative effect of change in accounting principles
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect reduction to retained earnings			53,880
Allowance for loan losses on PCI loans		$ 80,915
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect reduction to retained earnings	$ (535,375)		(543,800)	$ (426,942)	$ (393,674)
Retained Earnings | Cumulative effect of change in accounting principles
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect reduction to retained earnings			$ 53,880

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - CECL (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	$ 165,827	$ 87,820	$ 87,820	$ 58,403	$ 51,461
Allowance for credit losses on off-balance-sheet credit exposures	1,113	0	0	0	0
Commercial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	48,863	27,311	27,311	17,342	12,844
Real estate | Commercial Real Estate, Construction, Land and Land Development
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	103,573	50,123	50,123	34,083	33,085
Real estate | Residential Real Estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	4,401	6,786	6,786	4,437	3,678
Real estate | Single-family interim construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	8,328	2,156	2,156	1,831	1,606
Agricultural
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	108	337	337	345	332
Consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	353	442	442	263	226
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	201	242	242	60	5
Unallocated
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss	$ 0	423	423	$ 42	(315)
Cumulative effect of change in accounting principles
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		80,915
Allowance for credit losses on off-balance-sheet credit exposures		1,113	$ 1,113		$ 0
Cumulative effect of change in accounting principles | Commercial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		17,103
Cumulative effect of change in accounting principles | Real estate | Commercial Real Estate, Construction, Land and Land Development
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		59,683
Cumulative effect of change in accounting principles | Real estate | Residential Real Estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		(2,115)
Cumulative effect of change in accounting principles | Real estate | Single-family interim construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		7,179
Cumulative effect of change in accounting principles | Agricultural
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		(178)
Cumulative effect of change in accounting principles | Consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		(110)
Cumulative effect of change in accounting principles | Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		(224)
Cumulative effect of change in accounting principles | Unallocated
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		(423)
Adjusted beginning balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		168,735
Allowance for credit losses on off-balance-sheet credit exposures		1,113
Adjusted beginning balance | Commercial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		44,414
Adjusted beginning balance | Real estate | Commercial Real Estate, Construction, Land and Land Development
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		109,806
Adjusted beginning balance | Real estate | Residential Real Estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		4,671
Adjusted beginning balance | Real estate | Single-family interim construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		9,335
Adjusted beginning balance | Agricultural
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		159
Adjusted beginning balance | Consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		332
Adjusted beginning balance | Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		18
Adjusted beginning balance | Unallocated
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Credit Loss		$ 0

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic earnings per share:
Net income	$ 59,980	$ 44,167
Less: Undistributed earnings allocated to participating securities	487	209
Less: Dividends paid on participating securities	134	68
Net income available to common shareholders	$ 59,359	$ 43,890
Weighted average basic shares outstanding (shares)	42,731,456	42,741,399
Basic earnings per share (usd per share)	$ 1.39	$ 1.03
Diluted earnings per share:
Total weighted average diluted shares outstanding (shares)	42,775,777	42,749,958
Diluted earnings per share (usd per share)	$ 1.39	$ 1.03
Anti-dilutive participating securities (shares)	202,811	0
Performance stock units
Diluted earnings per share:
Add dilutive (shares)	44,321	0
Participating Securities
Diluted earnings per share:
Add dilutive (shares)	0	8,559

Statement of Cash Flows - Other

Statement of Cash Flows - Other Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash transactions:
Interest expense paid	$ 21,785	$ 35,400
Income taxes paid	8	0
Noncash transactions:
Deferred dividend equivalents	82	0
Transfers of loans to other real estate owned	0	3,914
Loans to facilitate the sale of other real estate owned	0	1,564
Securities purchased, not yet settled	5,000	0
Right-of-use assets obtained in exchange for lease liabilities	57	0
Transfer of premises and equipment to other assets	$ 88	$ 0

Securities Available for Sale -

Securities Available for Sale - Amortized Cost of Securities and Approximate Fair Values (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	$ 1,284,280	$ 1,108,453
Gross Unrealized Gains	38,608	47,271
Gross Unrealized Losses	(14,931)	(2,031)
Fair Value	1,307,957	1,153,693
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Accrued Interest Receivable	5,206	6,242
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	33,051	43,060
Gross Unrealized Gains	1,401	1,648
Gross Unrealized Losses	0	0
Fair Value	34,452	44,708
Government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	295,580	247,764
Gross Unrealized Gains	2,806	3,169
Gross Unrealized Losses	(8,746)	(1,916)
Fair Value	289,640	249,017
Obligations of state and municipal subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	373,045	373,017
Gross Unrealized Gains	16,044	20,168
Gross Unrealized Losses	(1,233)	(20)
Fair Value	387,856	393,165
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	28,494	21,496
Gross Unrealized Gains	580	608
Gross Unrealized Losses	(79)	(2)
Fair Value	28,995	22,102
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	552,910	421,916
Gross Unrealized Gains	17,777	21,678
Gross Unrealized Losses	(4,873)	(93)
Fair Value	565,814	443,501
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost (1)	1,200	1,200
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 1,200	$ 1,200

Securities Available for Sale_2

Securities Available for Sale - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Abstract]
Carrying value of securities pledged	$ 779,138	$ 738,519
Available-for-sale, Allowance for Credit Loss	$ 0

Securities Available for Sale_3

Securities Available for Sale - Proceeds, Gross Gains and Gross Losses from Sale (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Securities, Available-for-sale [Abstract]
Proceeds from sale	$ 0	$ 13,100
Gross gains	0	359
Gross losses	$ 0	$ 3

Securities Available for Sale_4

Securities Available for Sale - Amortized Cost and Estimated Fair Value of Securities Available for Sale by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized Cost (1)
Due in one year or less	$ 27,652
Due from one year to five years	137,914
Due from five to ten years	247,804
Thereafter	318,000
Total	731,370
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA	552,910
Amortized Cost (1)	1,284,280	$ 1,108,453
Fair Value
Due in one year or less	27,986
Due from one year to five years	143,780
Due from five to ten years	249,486
Thereafter	320,891
Total	742,143
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA	565,814
Fair Value	$ 1,307,957	$ 1,153,693

Securities Available for Sale_5

Securities Available for Sale - Summary of Unrealized Losses and Fair Value of Securities in Continuous Unrealized Loss Positions (Details) $ in Thousands	Mar. 31, 2021USD ($)security	Dec. 31, 2020USD ($)security
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	79	33
Less than 12 months: estimated fair value	$ 422,306	$ 159,025
Less than 12 months: unrealized losses	$ (14,931)	$ (2,031)
Greater than 12 months: number of securities | security	0	0
Greater than 12 months: estimated fair value	$ 0	$ 0
Greater than 12 months: unrealized losses	0	0
Total: estimated fair value	422,306	159,025
Total: unrealized losses	$ (14,931)	$ (2,031)
Government agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	31	20
Less than 12 months: estimated fair value	$ 181,215	$ 112,897
Less than 12 months: unrealized losses	$ (8,746)	$ (1,916)
Greater than 12 months: number of securities | security	0	0
Greater than 12 months: estimated fair value	$ 0	$ 0
Greater than 12 months: unrealized losses	0	0
Total: estimated fair value	181,215	112,897
Total: unrealized losses	$ (8,746)	$ (1,916)
Obligations of state and municipal subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	12	2
Less than 12 months: estimated fair value	$ 46,956	$ 3,786
Less than 12 months: unrealized losses	$ (1,233)	$ (20)
Greater than 12 months: number of securities | security	0	0
Greater than 12 months: estimated fair value	$ 0	$ 0
Greater than 12 months: unrealized losses	0	0
Total: estimated fair value	46,956	3,786
Total: unrealized losses	$ (1,233)	$ (20)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	3	1
Less than 12 months: estimated fair value	$ 5,421	$ 998
Less than 12 months: unrealized losses	$ (79)	$ (2)
Greater than 12 months: number of securities | security	0	0
Greater than 12 months: estimated fair value	$ 0	$ 0
Greater than 12 months: unrealized losses	0	0
Total: estimated fair value	5,421	998
Total: unrealized losses	$ (79)	$ (2)
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA
Debt Securities, Available-for-sale [Line Items]
Less than 12 months: number of securities | security	33	10
Less than 12 months: estimated fair value	$ 188,714	$ 41,344
Less than 12 months: unrealized losses	$ (4,873)	$ (93)
Greater than 12 months: number of securities | security	0	0
Greater than 12 months: estimated fair value	$ 0	$ 0
Greater than 12 months: unrealized losses	0	0
Total: estimated fair value	188,714	41,344
Total: unrealized losses	$ (4,873)	$ (93)

Loans, Net and Allowance for _3

Loans, Net and Allowance for Credit Losses on Loans - Composition of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 12,770,757
Loans			$ 13,076,095
Deferred loan fees, net	(15,450)		(10,037)
Allowance for credit losses	(165,827)	$ (87,820)	(87,820)	$ (58,403)	$ (51,461)
Total loans, net	12,604,930		12,978,238
Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued Interest Receivable	54,683		54,328
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,596,654
Loans			3,902,266
Allowance for credit losses	(48,863)	(27,311)	(27,311)	(17,342)	(12,844)
Real estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,194,353
Loans			6,096,676
Real estate | Commercial construction, land and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,206,350
Loans			1,245,801
Real estate | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,310,371
Loans			1,352,465
Allowance for credit losses	(4,401)	(6,786)	(6,786)	(4,437)	(3,678)
Real estate | Single-family interim construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	312,975
Loans			326,575
Allowance for credit losses	(8,328)	(2,156)	(2,156)	(1,831)	(1,606)
Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	74,820
Loans			85,014
Allowance for credit losses	(108)	(337)	(337)	(345)	(332)
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	74,923
Loans			66,952
Allowance for credit losses	(353)	(442)	(442)	(263)	(226)
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	311
Loans			346
Allowance for credit losses	$ (201)	$ (242)	$ (242)	$ (60)	$ (5)

Loans, Net and Allowance for _4

Loans, Net and Allowance for Credit Losses on Loans - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021USD ($)modified_loan	Mar. 31, 2020USD ($)modified_loan	Jan. 01, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged	$ 6,721,999,000			$ 6,743,350,000
Loans, net	12,604,930,000			12,978,238,000
Troubled debt restructuring modification recorded investment	$ 2,549,000			2,564,000
Number of loans modified under troubled debt restructurings that subsequently defaulted | modified_loan	0	0
Commitments to lend	$ 0	$ 0
Allowance for loan losses on PCI loans	165,827,000	58,403,000	$ 87,820,000	87,820,000	$ 51,461,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses on PCI loans	$ 48,863,000	17,342,000	27,311,000	27,311,000	12,844,000
Commercial | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP interest rate	1.00%
PPP loans outstanding	$ 912,176,000			804,397,000
PPP deferred loan fees	14,533,000			9,770,000
Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses on PCI loans	$ 108,000	345,000	337,000	337,000	332,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of the portfolio	1.00%
Allowance for loan losses on PCI loans	$ 353,000	$ 263,000	$ 442,000	442,000	$ 226,000
Geographic Concentration Risk | Loans and Leases, Net | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of the portfolio	27.00%
Maximum | Commercial | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP term	5 years
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans requiring external review (greater than)	$ 3,000,000
Minimum | Commercial | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP term	2 years
Energy Related Loans | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	$ 202,145,000			205,496,000
Warehouse Loans | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net	$ 1,105,699,000			$ 1,453,797,000
Duration of the loans to larger mortgage originators	60 days
Warehouse Loans | Maximum | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Duration of the loans to mortgage bankers	15 days
Owner Occupied | Loans and Leases, Net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of the portfolio	28.00%
Real Estate Loan | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan to value ratio (percent)	80.00%
Loan, amortization period	20 years
Non-Real Estate Loan | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of operating lines	1 year

Loans, Net and Allowance for _5

Loans, Net and Allowance for Credit Losses on Loans - Rollforward of Activity in Credit Losses (Details) - USD ($) $ in Thousands	Jan. 01, 2021	Mar. 31, 2021	Mar. 31, 2020
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 87,820	$ 87,820	$ 51,461
Provision for credit losses		(2,500)	8,381
Charge-offs		(446)	(1,509)
Recoveries		38	70
Balance at end of period	87,820	165,827	58,403
Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	67,880
Initial allowance on loans purchased with credit deterioration	13,035
Balance at end of period	80,915
Commercial
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	27,311	27,311	12,844
Provision for credit losses		4,501	5,053
Charge-offs		(70)	(571)
Recoveries		18	16
Balance at end of period	27,311	48,863	17,342
Commercial | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	12,775
Initial allowance on loans purchased with credit deterioration	4,328
Balance at end of period	17,103
Real estate | Commercial Real Estate, Construction, Land and Land Development
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	50,123	50,123	33,085
Provision for credit losses		(5,932)	1,733
Charge-offs		(301)	(735)
Recoveries		0	0
Balance at end of period	50,123	103,573	34,083
Real estate | Commercial Real Estate, Construction, Land and Land Development | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	51,116
Initial allowance on loans purchased with credit deterioration	8,567
Balance at end of period	59,683
Real estate | Residential Real Estate
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	6,786	6,786	3,678
Provision for credit losses		(270)	759
Charge-offs		0	0
Recoveries		0	0
Balance at end of period	6,786	4,401	4,437
Real estate | Residential Real Estate | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	(2,255)
Initial allowance on loans purchased with credit deterioration	140
Balance at end of period	(2,115)
Real estate | Single-family interim construction
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,156	2,156	1,606
Provision for credit losses		(1,007)	307
Charge-offs		0	(82)
Recoveries		0	0
Balance at end of period	2,156	8,328	1,831
Real estate | Single-family interim construction | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	7,179
Initial allowance on loans purchased with credit deterioration	0
Balance at end of period	7,179
Agricultural
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	337	337	332
Provision for credit losses		(51)	13
Charge-offs		0	0
Recoveries		0	0
Balance at end of period	337	108	345
Agricultural | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	(178)
Initial allowance on loans purchased with credit deterioration	0
Balance at end of period	(178)
Consumer
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	442	442	226
Provision for credit losses		36	28
Charge-offs		(18)	(9)
Recoveries		3	18
Balance at end of period	442	353	263
Consumer | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	(110)
Initial allowance on loans purchased with credit deterioration	0
Balance at end of period	(110)
Other
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	242	242	5
Provision for credit losses		223	131
Charge-offs		(57)	(112)
Recoveries		17	36
Balance at end of period	242	201	60
Other | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	(224)
Initial allowance on loans purchased with credit deterioration	0
Balance at end of period	(224)
Unallocated
Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	423	423	(315)
Provision for credit losses		0	357
Charge-offs		0	0
Recoveries		0	0
Balance at end of period	423	$ 0	$ 42
Unallocated | Cumulative effect of change in accounting principles
Allowance for Credit Loss [Roll Forward]
Impact of adopting ASC 326	(423)
Initial allowance on loans purchased with credit deterioration	0
Balance at end of period	$ (423)

Loans, Net and Allowance for _6

Loans, Net and Allowance for Credit Losses on Loans - Individually Evaluated Loans by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	$ 72,144	$ 64,383
Specific allocations of individually evaluated loans	19,811	8,524
Commercial
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	44,933	39,298
Specific allocations of individually evaluated loans	15,948	8,281
Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	27,211	21,880
Specific allocations of individually evaluated loans	3,863	243
Real estate | Residential Real Estate
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	0	2,550
Specific allocations of individually evaluated loans	0	0
Real estate | Single-family interim construction
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	0	0
Specific allocations of individually evaluated loans	0	0
Agricultural
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	0	613
Specific allocations of individually evaluated loans	0	0
Consumer
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	0	42
Specific allocations of individually evaluated loans	0	0
Other
Financing Receivable, Impaired [Line Items]
Individually evaluated loans	0	0
Specific allocations of individually evaluated loans	$ 0	$ 0

Loans, Net and Allowance for _7

Loans, Net and Allowance for Credit Losses on Loans - Summary of Non Performing Loans by Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	$ 2,549	$ 2,564
Nonaccrual, No Allowance	3,016
Financing Receivable, Nonaccrual, Interest Income	0
Nonperforming Financial Instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	58,090	48,997
Loans past due 90 days and still accruing	316	433
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	1,959	1,986
Total nonperforming loans	60,365	51,416
Nonperforming Financial Instruments | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	32,912	25,898
Loans past due 90 days and still accruing	316	433
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	33,228	26,331
Nonperforming Financial Instruments | Real estate | Commercial Real Estate, Construction, Land and Land Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	22,312	20,072
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	1,786	1,808
Total nonperforming loans	24,098	21,880
Nonperforming Financial Instruments | Real estate | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	2,289	2,372
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	173	178
Total nonperforming loans	2,462	2,550
Nonperforming Financial Instruments | Real estate | Single-family interim construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	0	0
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	0	0
Nonperforming Financial Instruments | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	551	613
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	551	613
Nonperforming Financial Instruments | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	26	42
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	26	42
Nonperforming Financial Instruments | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual Loans	0	0
Loans past due 90 days and still accruing	0	0
Troubled debt restructurings (not included in nonaccrual or loans past due and still accruing)	0	0
Total nonperforming loans	$ 0	$ 0

Loans, Net and Allowance for _8

Loans, Net and Allowance for Credit Losses on Loans - Summary of Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)contract	Mar. 31, 2020USD ($)contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	1	1
Pre-restructuring outstanding recorded investment	$ 49	$ 1,517
Post-restructuring outstanding recorded investment	$ 44	$ 1,517
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	1	0
Pre-restructuring outstanding recorded investment	$ 49	$ 0
Post-restructuring outstanding recorded investment	$ 44	$ 0
Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	0	1
Pre-restructuring outstanding recorded investment	$ 0	$ 1,517
Post-restructuring outstanding recorded investment	$ 0	$ 1,517
Real estate | Residential Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Real estate | Single-family interim construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Agricultural
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans modified under troubled debt restructuring | contract	0	0
Pre-restructuring outstanding recorded investment	$ 0	$ 0
Post-restructuring outstanding recorded investment	$ 0	$ 0

Loans, Net and Allowance for _9

Loans, Net and Allowance for Credit Losses on Loans - Aging of Past Due Loans by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans past due	$ 48,710	$ 45,881
Current Loans	12,722,047	13,030,214
Total Loans		13,076,095
Total Loans	12,770,757
Acquired with deteriorated credit quality
Financing Receivable, Past Due [Line Items]
Loans past due		3,843
Current Loans		210,943
Total Loans		214,786
Commercial
Financing Receivable, Past Due [Line Items]
Loans past due	21,607
Current Loans	3,575,047
Total Loans		3,902,266
Total Loans	3,596,654
Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Past Due [Line Items]
Loans past due	22,067
Current Loans	7,378,636
Total Loans	7,400,703
Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans past due	4,532
Current Loans	1,305,839
Total Loans		1,352,465
Total Loans	1,310,371
Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Loans past due	355
Current Loans	312,620
Total Loans		326,575
Total Loans	312,975
Agricultural
Financing Receivable, Past Due [Line Items]
Loans past due	37
Current Loans	74,783
Total Loans		85,014
Total Loans	74,820
Consumer
Financing Receivable, Past Due [Line Items]
Loans past due	112
Current Loans	74,811
Total Loans		66,952
Total Loans	74,923
Other
Financing Receivable, Past Due [Line Items]
Loans past due	0
Current Loans	311
Total Loans		346
Total Loans	311
Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans past due	11,066	11,575
Loans 30-89 Days Past Due | Acquired with deteriorated credit quality
Financing Receivable, Past Due [Line Items]
Loans past due		624
Loans 30-89 Days Past Due | Commercial
Financing Receivable, Past Due [Line Items]
Loans past due	1,185
Loans 30-89 Days Past Due | Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Past Due [Line Items]
Loans past due	6,223
Loans 30-89 Days Past Due | Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans past due	3,175
Loans 30-89 Days Past Due | Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Loans past due	355
Loans 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Loans past due	37
Loans 30-89 Days Past Due | Consumer
Financing Receivable, Past Due [Line Items]
Loans past due	91
Loans 30-89 Days Past Due | Other
Financing Receivable, Past Due [Line Items]
Loans past due	0
Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans past due	37,644	34,306
Loans 90 Days or More Past Due | Acquired with deteriorated credit quality
Financing Receivable, Past Due [Line Items]
Loans past due		3,219
Loans 90 Days or More Past Due | Commercial
Financing Receivable, Past Due [Line Items]
Loans past due	20,422
Loans 90 Days or More Past Due | Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Past Due [Line Items]
Loans past due	15,844
Loans 90 Days or More Past Due | Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans past due	1,357
Loans 90 Days or More Past Due | Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Loans past due	0
Loans 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Loans past due	0
Loans 90 Days or More Past Due | Consumer
Financing Receivable, Past Due [Line Items]
Loans past due	21
Loans 90 Days or More Past Due | Other
Financing Receivable, Past Due [Line Items]
Loans past due	$ 0
Receivables, excluding receivables acquired with deteriorated credit quality
Financing Receivable, Past Due [Line Items]
Loans past due		42,038
Current Loans		12,819,271
Total Loans		12,861,309
Receivables, excluding receivables acquired with deteriorated credit quality | Commercial
Financing Receivable, Past Due [Line Items]
Loans past due		16,470
Current Loans		3,846,810
Total Loans		3,863,280
Receivables, excluding receivables acquired with deteriorated credit quality | Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Past Due [Line Items]
Loans past due		19,243
Current Loans		7,152,247
Total Loans		7,171,490
Receivables, excluding receivables acquired with deteriorated credit quality | Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans past due		6,197
Current Loans		1,341,587
Total Loans		1,347,784
Receivables, excluding receivables acquired with deteriorated credit quality | Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Loans past due		0
Current Loans		326,575
Total Loans		326,575
Receivables, excluding receivables acquired with deteriorated credit quality | Agricultural
Financing Receivable, Past Due [Line Items]
Loans past due		1
Current Loans		84,896
Total Loans		84,897
Receivables, excluding receivables acquired with deteriorated credit quality | Consumer
Financing Receivable, Past Due [Line Items]
Loans past due		127
Current Loans		66,810
Total Loans		66,937
Receivables, excluding receivables acquired with deteriorated credit quality | Other
Financing Receivable, Past Due [Line Items]
Loans past due		0
Current Loans		346
Total Loans		346
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans past due		10,951
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Commercial
Financing Receivable, Past Due [Line Items]
Loans past due		3,243
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Past Due [Line Items]
Loans past due		2,453
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans past due		5,169
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Loans past due		0
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Loans past due		0
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Consumer
Financing Receivable, Past Due [Line Items]
Loans past due		86
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 30-89 Days Past Due | Other
Financing Receivable, Past Due [Line Items]
Loans past due		0
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans past due		31,087
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Commercial
Financing Receivable, Past Due [Line Items]
Loans past due		13,227
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Past Due [Line Items]
Loans past due		16,790
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Loans past due		1,028
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Real estate | Single-family interim construction
Financing Receivable, Past Due [Line Items]
Loans past due		0
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Loans past due		1
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Consumer
Financing Receivable, Past Due [Line Items]
Loans past due		41
Receivables, excluding receivables acquired with deteriorated credit quality | Loans 90 Days or More Past Due | Other
Financing Receivable, Past Due [Line Items]
Loans past due		$ 0

Loans, Net and Allowance for_10

Loans, Net and Allowance for Credit Losses on Loans - Loans held for investment by year of origination and internally assigned credit grade (Details) $ in Thousands	Mar. 31, 2021USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 12,770,757
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	295,743
Term Loans by Year of Origination, 2020	944,409
Term Loans by Year of Origination, 2019	215,876
Term Loans by Year of Origination, 2018	165,041
Term Loans by Year of Origination, 2017	147,872
Term Loans by Year of Origination, Prior	175,351
Revolving Loans	1,647,757
Revolving Loans Converted to Term Loans	4,605
Total Loans	3,596,654
Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	282,123
Term Loans by Year of Origination, 2020	937,698
Term Loans by Year of Origination, 2019	159,944
Term Loans by Year of Origination, 2018	138,458
Term Loans by Year of Origination, 2017	128,778
Term Loans by Year of Origination, Prior	156,849
Revolving Loans	1,571,377
Revolving Loans Converted to Term Loans	3,269
Total Loans	3,378,496
Commercial | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	472
Term Loans by Year of Origination, 2020	1,922
Term Loans by Year of Origination, 2019	1,650
Term Loans by Year of Origination, 2018	10,446
Term Loans by Year of Origination, 2017	9,389
Term Loans by Year of Origination, Prior	99
Revolving Loans	44,719
Revolving Loans Converted to Term Loans	1,336
Total Loans	70,033
Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	3,938
Term Loans by Year of Origination, 2019	19,103
Term Loans by Year of Origination, 2018	7,959
Term Loans by Year of Origination, 2017	443
Term Loans by Year of Origination, Prior	1,020
Revolving Loans	3,023
Revolving Loans Converted to Term Loans	0
Total Loans	35,486
Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	13,148
Term Loans by Year of Origination, 2020	851
Term Loans by Year of Origination, 2019	33,434
Term Loans by Year of Origination, 2018	8,178
Term Loans by Year of Origination, 2017	9,262
Term Loans by Year of Origination, Prior	17,383
Revolving Loans	18,474
Revolving Loans Converted to Term Loans	0
Total Loans	100,730
Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	1,745
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	10,164
Revolving Loans Converted to Term Loans	0
Total Loans	11,909
Real estate | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	468,338
Term Loans by Year of Origination, 2020	1,580,166
Term Loans by Year of Origination, 2019	1,082,382
Term Loans by Year of Origination, 2018	998,330
Term Loans by Year of Origination, 2017	835,239
Term Loans by Year of Origination, Prior	1,164,791
Revolving Loans	64,272
Revolving Loans Converted to Term Loans	835
Total Loans	6,194,353
Real estate | Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	396,430
Term Loans by Year of Origination, 2020	1,440,420
Term Loans by Year of Origination, 2019	968,483
Term Loans by Year of Origination, 2018	835,598
Term Loans by Year of Origination, 2017	746,267
Term Loans by Year of Origination, Prior	1,005,653
Revolving Loans	62,697
Revolving Loans Converted to Term Loans	336
Total Loans	5,455,884
Real estate | Commercial | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	47,331
Term Loans by Year of Origination, 2020	47,901
Term Loans by Year of Origination, 2019	70,961
Term Loans by Year of Origination, 2018	81,980
Term Loans by Year of Origination, 2017	34,548
Term Loans by Year of Origination, Prior	73,083
Revolving Loans	1
Revolving Loans Converted to Term Loans	499
Total Loans	356,304
Real estate | Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	7,960
Term Loans by Year of Origination, 2020	54,141
Term Loans by Year of Origination, 2019	40,520
Term Loans by Year of Origination, 2018	77,624
Term Loans by Year of Origination, 2017	52,831
Term Loans by Year of Origination, Prior	54,845
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	287,921
Real estate | Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	16,617
Term Loans by Year of Origination, 2020	37,704
Term Loans by Year of Origination, 2019	2,418
Term Loans by Year of Origination, 2018	3,128
Term Loans by Year of Origination, 2017	1,593
Term Loans by Year of Origination, Prior	31,210
Revolving Loans	1,574
Revolving Loans Converted to Term Loans	0
Total Loans	94,244
Real estate | Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Real estate | Commercial construction, land and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	165,509
Term Loans by Year of Origination, 2020	390,141
Term Loans by Year of Origination, 2019	356,490
Term Loans by Year of Origination, 2018	216,222
Term Loans by Year of Origination, 2017	46,055
Term Loans by Year of Origination, Prior	22,286
Revolving Loans	9,647
Revolving Loans Converted to Term Loans	0
Total Loans	1,206,350
Real estate | Commercial construction, land and land development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	151,932
Term Loans by Year of Origination, 2020	365,287
Term Loans by Year of Origination, 2019	310,392
Term Loans by Year of Origination, 2018	177,927
Term Loans by Year of Origination, 2017	25,629
Term Loans by Year of Origination, Prior	20,017
Revolving Loans	9,647
Revolving Loans Converted to Term Loans	0
Total Loans	1,060,831
Real estate | Commercial construction, land and land development | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	1,984
Term Loans by Year of Origination, 2020	4,659
Term Loans by Year of Origination, 2019	28,682
Term Loans by Year of Origination, 2018	18,227
Term Loans by Year of Origination, 2017	10,397
Term Loans by Year of Origination, Prior	272
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	64,221
Real estate | Commercial construction, land and land development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	16,205
Term Loans by Year of Origination, 2019	15,981
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	9,999
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	42,185
Real estate | Commercial construction, land and land development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	11,593
Term Loans by Year of Origination, 2020	3,990
Term Loans by Year of Origination, 2019	1,435
Term Loans by Year of Origination, 2018	20,068
Term Loans by Year of Origination, 2017	30
Term Loans by Year of Origination, Prior	1,997
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	39,113
Real estate | Commercial construction, land and land development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Real estate | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	79,399
Term Loans by Year of Origination, 2020	345,810
Term Loans by Year of Origination, 2019	272,519
Term Loans by Year of Origination, 2018	169,530
Term Loans by Year of Origination, 2017	129,090
Term Loans by Year of Origination, Prior	252,248
Revolving Loans	60,313
Revolving Loans Converted to Term Loans	1,462
Total Loans	1,310,371
Real estate | Residential Real Estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	77,163
Term Loans by Year of Origination, 2020	343,414
Term Loans by Year of Origination, 2019	270,486
Term Loans by Year of Origination, 2018	167,961
Term Loans by Year of Origination, 2017	127,440
Term Loans by Year of Origination, Prior	242,257
Revolving Loans	59,961
Revolving Loans Converted to Term Loans	1,462
Total Loans	1,290,144
Real estate | Residential Real Estate | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	649
Term Loans by Year of Origination, 2020	594
Term Loans by Year of Origination, 2019	1,419
Term Loans by Year of Origination, 2018	423
Term Loans by Year of Origination, 2017	548
Term Loans by Year of Origination, Prior	5,860
Revolving Loans	65
Revolving Loans Converted to Term Loans	0
Total Loans	9,558
Real estate | Residential Real Estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	1,398
Term Loans by Year of Origination, 2020	1,154
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	133
Term Loans by Year of Origination, 2017	260
Term Loans by Year of Origination, Prior	1,174
Revolving Loans	230
Revolving Loans Converted to Term Loans	0
Total Loans	4,349
Real estate | Residential Real Estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	189
Term Loans by Year of Origination, 2020	648
Term Loans by Year of Origination, 2019	614
Term Loans by Year of Origination, 2018	1,013
Term Loans by Year of Origination, 2017	842
Term Loans by Year of Origination, Prior	2,957
Revolving Loans	57
Revolving Loans Converted to Term Loans	0
Total Loans	6,320
Real estate | Residential Real Estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Real estate | Single-family interim construction
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	62,725
Term Loans by Year of Origination, 2020	210,042
Term Loans by Year of Origination, 2019	26,092
Term Loans by Year of Origination, 2018	363
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	380
Revolving Loans	13,373
Revolving Loans Converted to Term Loans	0
Total Loans	312,975
Real estate | Single-family interim construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	62,725
Term Loans by Year of Origination, 2020	209,338
Term Loans by Year of Origination, 2019	26,092
Term Loans by Year of Origination, 2018	363
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	380
Revolving Loans	13,373
Revolving Loans Converted to Term Loans	0
Total Loans	312,271
Real estate | Single-family interim construction | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	704
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	704
Real estate | Single-family interim construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Real estate | Single-family interim construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Real estate | Single-family interim construction | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	3,043
Term Loans by Year of Origination, 2020	22,083
Term Loans by Year of Origination, 2019	6,597
Term Loans by Year of Origination, 2018	10,448
Term Loans by Year of Origination, 2017	15,889
Term Loans by Year of Origination, Prior	7,368
Revolving Loans	9,392
Revolving Loans Converted to Term Loans	0
Total Loans	74,820
Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	3,041
Term Loans by Year of Origination, 2020	21,531
Term Loans by Year of Origination, 2019	4,899
Term Loans by Year of Origination, 2018	10,382
Term Loans by Year of Origination, 2017	14,889
Term Loans by Year of Origination, Prior	6,620
Revolving Loans	6,547
Revolving Loans Converted to Term Loans	0
Total Loans	67,909
Agricultural | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	552
Term Loans by Year of Origination, 2019	1,698
Term Loans by Year of Origination, 2018	66
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	146
Revolving Loans	2,509
Revolving Loans Converted to Term Loans	0
Total Loans	4,971
Agricultural | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	1,000
Term Loans by Year of Origination, Prior	0
Revolving Loans	336
Revolving Loans Converted to Term Loans	0
Total Loans	1,336
Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	2
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	602
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	604
Agricultural | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	2,486
Term Loans by Year of Origination, 2020	13,664
Term Loans by Year of Origination, 2019	3,900
Term Loans by Year of Origination, 2018	1,911
Term Loans by Year of Origination, 2017	775
Term Loans by Year of Origination, Prior	673
Revolving Loans	51,464
Revolving Loans Converted to Term Loans	50
Total Loans	74,923
Consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	2,486
Term Loans by Year of Origination, 2020	13,632
Term Loans by Year of Origination, 2019	3,893
Term Loans by Year of Origination, 2018	1,911
Term Loans by Year of Origination, 2017	758
Term Loans by Year of Origination, Prior	640
Revolving Loans	51,464
Revolving Loans Converted to Term Loans	50
Total Loans	74,834
Consumer | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	4
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	4
Consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	32
Term Loans by Year of Origination, 2019	7
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	13
Term Loans by Year of Origination, Prior	33
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	85
Consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	311
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	311
Other | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	311
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	311
Other | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Other | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Other | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	0
Other | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Year of Origination, 2021	0
Term Loans by Year of Origination, 2020	0
Term Loans by Year of Origination, 2019	0
Term Loans by Year of Origination, 2018	0
Term Loans by Year of Origination, 2017	0
Term Loans by Year of Origination, Prior	0
Revolving Loans	0
Revolving Loans Converted to Term Loans	0
Total Loans	$ 0

Loans, Net and Allowance for_11

Loans, Net and Allowance for Credit Losses on Loans - Summary of Loans by Credit Quality Indicator (Details) $ in Thousands	Dec. 31, 2020USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 13,076,095
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,006,267
Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	424,143
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	406,080
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	229,514
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,091
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,902,266
Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,700,626
Commercial | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	55,960
Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	38,186
Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	97,403
Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,091
Real estate | Commercial Real Estate, Construction, Land and Land Development
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,342,477
Real estate | Commercial Real Estate, Construction, Land and Land Development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,504,933
Real estate | Commercial Real Estate, Construction, Land and Land Development | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	352,910
Real estate | Commercial Real Estate, Construction, Land and Land Development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	360,963
Real estate | Commercial Real Estate, Construction, Land and Land Development | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	123,671
Real estate | Commercial Real Estate, Construction, Land and Land Development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Real estate | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,352,465
Real estate | Residential Real Estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,332,757
Real estate | Residential Real Estate | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,296
Real estate | Residential Real Estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	5,726
Real estate | Residential Real Estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,686
Real estate | Residential Real Estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Real estate | Single-family interim construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	326,575
Real estate | Single-family interim construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	323,800
Real estate | Single-family interim construction | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,775
Real estate | Single-family interim construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Real estate | Single-family interim construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Real estate | Single-family interim construction | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	85,014
Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	76,951
Agricultural | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,194
Agricultural | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,205
Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	664
Agricultural | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	66,952
Consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	66,854
Consumer | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	8
Consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	90
Consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	346
Other | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	346
Other | Pass/ Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Other | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Other | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0
Other | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0

Off-Balance Sheet Arrangement_3

Off-Balance Sheet Arrangements, Commitments and Contingencies (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 2,364,146	$ 2,294,133
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	2,338,297	2,268,216
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 25,849	$ 25,917

Off-Balance Sheet Arrangement_4

Off-Balance Sheet Arrangements, Commitments and Contingencies - Allowance for Off-Balance Sheet Credit Exposure (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period	$ 0	$ 0
Provision for off-balance sheet credit exposure	0	0
Balance at end of period	1,113	0
Cumulative effect of change in accounting principles
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period	$ 1,113	$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income tax expense for the period	$ 15,745	$ 10,836
Effective tax rate (percent)	20.80%	19.70%

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	$ 1,307,957,000	$ 1,153,693,000
Loans held for sale, fair value option	53,930,000	71,769,000
Aggregate principal balance of loans held for sale	53,030,000	68,670,000
Loans held for sale, 90 days or greater past due	0
Loans held for sale, non-accrual	0
Not designated as hedging | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Loans held for sale, fair value option	53,930,000	71,769,000
Not designated as hedging | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Loans held for sale, fair value option	0	0
Not designated as hedging | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Loans held for sale, fair value option	53,930,000	71,769,000
Not designated as hedging | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Loans held for sale, fair value option	0	0
Not designated as hedging | Interest rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	2,158,000	3,515,000
Derivative financial instruments - Liabilities	52,000	0
Not designated as hedging | Interest rate lock commitments | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	2,158,000	3,515,000
Derivative financial instruments - Liabilities	52,000
Not designated as hedging | Interest rate lock commitments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0	0
Derivative financial instruments - Liabilities	0
Not designated as hedging | Interest rate lock commitments | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	2,158,000	3,515,000
Derivative financial instruments - Liabilities	52,000
Not designated as hedging | Interest rate lock commitments | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0	0
Derivative financial instruments - Liabilities	0
Not designated as hedging | Forward mortgage-backed securities trades
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	787,000	0
Derivative financial instruments - Liabilities	9,000	568,000
Not designated as hedging | Forward mortgage-backed securities trades | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	787,000
Derivative financial instruments - Liabilities	9,000	568,000
Not designated as hedging | Forward mortgage-backed securities trades | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0
Derivative financial instruments - Liabilities	0	0
Not designated as hedging | Forward mortgage-backed securities trades | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	787,000
Derivative financial instruments - Liabilities	9,000	568,000
Not designated as hedging | Forward mortgage-backed securities trades | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0
Derivative financial instruments - Liabilities	0	0
Not designated as hedging | Interest Rate Swap | Loan customer counterparty | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	12,427,000	20,159,000
Derivative financial instruments - Liabilities	1,291,000
Not designated as hedging | Interest Rate Swap | Loan customer counterparty | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0	0
Derivative financial instruments - Liabilities	0
Not designated as hedging | Interest Rate Swap | Loan customer counterparty | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	12,427,000	20,159,000
Derivative financial instruments - Liabilities	1,291,000
Not designated as hedging | Interest Rate Swap | Loan customer counterparty | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0	0
Derivative financial instruments - Liabilities	0
Not designated as hedging | Interest Rate Swap | Financial institution counterparty | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	1,372,000
Derivative financial instruments - Liabilities	12,952,000	21,306,000
Not designated as hedging | Interest Rate Swap | Financial institution counterparty | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0
Derivative financial instruments - Liabilities	0	0
Not designated as hedging | Interest Rate Swap | Financial institution counterparty | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	1,372,000
Derivative financial instruments - Liabilities	12,952,000	21,306,000
Not designated as hedging | Interest Rate Swap | Financial institution counterparty | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Derivative financial instruments - Assets	0
Derivative financial instruments - Liabilities	0	0
U.S. treasuries
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	34,452,000	44,708,000
U.S. treasuries | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	34,452,000	44,708,000
U.S. treasuries | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
U.S. treasuries | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	34,452,000	44,708,000
U.S. treasuries | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	289,640,000	249,017,000
Government agency securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	289,640,000	249,017,000
Government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Government agency securities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	289,640,000	249,017,000
Government agency securities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Obligations of state and municipal subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	387,856,000	393,165,000
Obligations of state and municipal subdivisions | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	387,856,000	393,165,000
Obligations of state and municipal subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Obligations of state and municipal subdivisions | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	387,856,000	393,165,000
Obligations of state and municipal subdivisions | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	28,995,000	22,102,000
Corporate bonds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	28,995,000	22,102,000
Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Corporate bonds | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	28,995,000	22,102,000
Corporate bonds | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	565,814,000	443,501,000
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	565,814,000	443,501,000
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	565,814,000	443,501,000
Mortgage-backed securities guaranteed by FHLMC, FNMA and GNMA | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Other securities
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	1,200,000	1,200,000
Other securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	1,200,000	1,200,000
Other securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	0	0
Other securities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	1,200,000	1,200,000
Other securities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis
Securities available for sale	$ 0	$ 0

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets and Liabilities at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Individually evaluated loans	$ 72,144	$ 64,383
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Individually evaluated loans	12,481	16,903
Other real estate owned	0
Fair Value, Measurements, Nonrecurring | Individually evaluated loans
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Period Ended Total Losses	2,773	13,041
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Individually evaluated loans	0	0
Fair Value, Measurements, Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Individually evaluated loans	0	0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Individually evaluated loans	$ 12,481	$ 16,903

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	$ 2,364,146	$ 2,294,133
Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	2,338,297	2,268,216
Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	25,849	25,917
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	2,416,870	1,813,987
Certificates of deposit held in other banks	0	0
Loans held for sale, at cost	0	0
Loans, net	0	0
FHLB of Dallas stock and other restricted stock	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Accrued interest payable	0	0
FHLB advances	0	0
Other borrowings	0	0
Junior subordinated debentures	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Certificates of deposit held in other banks	4,569	4,595
Loans held for sale, at cost	3,963	11,138
Loans, net	0	0
FHLB of Dallas stock and other restricted stock	20,338	20,305
Accrued interest receivable	59,896	60,581
Financial liabilities:
Deposits	14,810,771	14,407,596
Accrued interest payable	3,654	7,397
FHLB advances	366,583	371,175
Other borrowings	327,350	327,150
Junior subordinated debentures	41,292	42,624
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Other Observable Inputs (Level 2) | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Certificates of deposit held in other banks	0	0
Loans held for sale, at cost	0	0
Loans, net	12,809,647	13,093,698
FHLB of Dallas stock and other restricted stock	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Accrued interest payable	0	0
FHLB advances	0	0
Other borrowings	0	0
Junior subordinated debentures	0	0
Significant Unobservable Inputs (Level 3) | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Significant Unobservable Inputs (Level 3) | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	2,416,870	1,813,987
Certificates of deposit held in other banks	4,482	4,482
Loans held for sale, at cost	3,869	10,878
Loans, net	12,604,930	12,978,238
FHLB of Dallas stock and other restricted stock	20,338	20,305
Accrued interest receivable	59,896	60,581
Financial liabilities:
Deposits	14,803,792	14,398,927
Accrued interest payable	3,654	7,397
FHLB advances	375,000	375,000
Other borrowings	308,350	312,175
Junior subordinated debentures	54,072	54,023
Carrying Amount | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Carrying Amount | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Estimated Fair Value
Financial assets:
Cash and cash equivalents	2,416,870	1,813,987
Certificates of deposit held in other banks	4,569	4,595
Loans held for sale, at cost	3,963	11,138
Loans, net	12,809,647	13,093,698
FHLB of Dallas stock and other restricted stock	20,338	20,305
Accrued interest receivable	59,896	60,581
Financial liabilities:
Deposits	14,810,771	14,407,596
Accrued interest payable	3,654	7,397
FHLB advances	366,583	371,175
Other borrowings	327,350	327,150
Junior subordinated debentures	41,292	42,624
Estimated Fair Value | Commitments to extend credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	0	0
Estimated Fair Value | Standby letters of credit
Off-balance sheet assets (liabilities):
Financial instruments with off-balance sheet risk	$ 0	$ 0

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Balances and Fair Values of Outstanding Positions (Details) - Not designated as hedging - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Interest rate lock commitments
Derivative [Line Items]
Outstanding Notional Balance	$ 90,496	$ 116,795
Asset Derivative Fair Value	2,158	3,515
Liability Derivative Fair Value	52	0
Forward mortgage-backed securities trades
Derivative [Line Items]
Outstanding Notional Balance	80,000	104,000
Asset Derivative Fair Value	787	0
Liability Derivative Fair Value	9	568
Commercial loan interest rate swaps | Commercial Loan | Loan customer counterparty
Derivative [Line Items]
Outstanding Notional Balance	323,760	335,370
Asset Derivative Fair Value	12,427	20,159
Liability Derivative Fair Value	1,291	0
Commercial loan interest rate swaps | Commercial Loan | Financial institution counterparty
Derivative [Line Items]
Outstanding Notional Balance	323,760	335,370
Asset Derivative Fair Value	1,372	0
Liability Derivative Fair Value	$ 12,952	$ 21,306

Derivative Financial Instrume_4

Derivative Financial Instruments - Schedule of Weighted Average Interest Rates (Details) - Commercial Loan - Not designated as hedging - Loan customer counterparty - Interest Rate Swap	Mar. 31, 2021	Dec. 31, 2020
Interest Rate Received
Derivative [Line Items]
Derivative, Average Fixed Interest Rate	4.08%	4.08%
Interest Rate Paid
Derivative [Line Items]
Derivative, Average Variable Interest Rate	2.28%	2.32%

Derivative Financial Instrume_5

Derivative Financial Instruments - Additional Information (Details)	Mar. 31, 2021USD ($)
Derivative [Line Items]
Cash collateral pledged for derivatives	$ 23,293,000
Securities collateral pledged for derivatives	$ 6,404,000
Risk Participation Agreements Participant Bank
Derivative [Line Items]
Number of risk participation agreements	1
Credit risk participation	$ 5,510,000
Risk Participation Agreements Lead Bank
Derivative [Line Items]
Number of risk participation agreements	1
Credit risk participation	$ 9,541,000
Loan customer counterparty | Interest Rate Swap
Derivative [Line Items]
Credit exposure limited to the net favorable value of all swaps	$ 13,799,000

Derivative Financial Instrume_6

Derivative Financial Instruments - Income (Loss) on Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest rate lock commitments
Derivative [Line Items]
Derivatives not designated as hedging instruments	$ (1,409)	$ 551
Forward mortgage-backed securities trades
Derivative [Line Items]
Derivatives not designated as hedging instruments	$ 1,346	$ (1,252)

Stock Awards - Additional Infor

Stock Awards - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Apr. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 2,496,000	$ 1,882,000
Estimated future compensation expense	$ 18,378,000
Period for recognition	2 years 6 months 18 days
Fair value of common stock awards vested	$ 6,875,000	4,198,000
Stock based compensation expense	3,206,000	1,882,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax expense (benefits) on vested restricted stock	$ (194,000)	$ 80,000
Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition	3 years 1 month 17 days
Unrecognized compensation expense	$ 3,964,000
Stock based compensation expense	710,000
Maximum | Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 6,315,000
2013 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (shares)			2,300,000
Remaining available for grant for future awards (shares)	1,071,629
2013 Equity Incentive Plan | Minimum | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period	1 year
2013 Equity Incentive Plan | Minimum | Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period	3 years
Stock based compensation, award vesting percentage	0.00%
2013 Equity Incentive Plan | Maximum | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period	5 years
2013 Equity Incentive Plan | Maximum | Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock vesting period	4 years
Stock based compensation, award vesting percentage	150.00%

Stock Awards - Nonvested Restri

Stock Awards - Nonvested Restricted Stock Awards Activity (Details) - Restricted Stock - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Number of Shares
Nonvested shares, beginning balance (shares)	468,800	284,861
Granted during the period (shares)	83,494	94,177
Vested during the period (shares)	(106,107)	(78,599)
Forfeited during the period (shares)	(4,506)
Nonvested shares, ending balance (shares)	441,681	300,439
Weighted Average Grant Date Fair Value
Nonvested shares, beginning balance (usd per share)	$ 49.01	$ 58.63
Granted during the period (usd per share)	63.36	53.48
Vested during the period (usd per share)	56.51	57.94
Forfeited during the period (usd per share)	53.26
Nonvested shares, ending balance (usd per share)	$ 49.88	$ 57.19

Stock Awards - Future Vesting S

Stock Awards - Future Vesting Schedule of Nonvested Shares (Details)	Mar. 31, 2021shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares (shares)	441,681
First year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares (shares)	174,575
Second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares (shares)	131,015
Third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares (shares)	83,160
Fourth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares (shares)	52,731
Fifth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested shares (shares)	200

Stock Awards - Schedule of Nonv

Stock Awards - Schedule of Nonvested Restricted Stock Awards (Details) - Performance stock units	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Number of Shares
Nonvested shares, beginning balance (shares) | shares	89,300
Granted during the period (shares) | shares	20,198
Nonvested shares, ending balance (shares) | shares	109,498
Weighted Average Grant Date Fair Value
Nonvested shares, beginning balance (usd per share) | $ / shares	$ 38.29
Granted during the period (usd per share) | $ / shares	62.58
Nonvested shares, ending balance (usd per share) | $ / shares	$ 42.77

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Cumulative effect reduction to retained earnings	$ (2,493,117,000)	$ (2,386,285,000)	$ (2,515,371,000)	$ (2,339,773,000)
Common stock repurchased	1,489,000	145,000
Common stock purchased to settle employee tax withholding related to vesting of stock awards	$ 1,489,000	$ 145,000
Common stock purchased to settle employee tax withholding related to vesting of stock awards (shares)	22,835	2,629
October 2020 Share Repurchase Program
Regulatory Assets [Line Items]
Share repurchase program authorized amount	$ 150,000,000
Common stock repurchased (shares)	109,548
Common stock repurchased	$ 5,660,000
Cumulative effect of change in accounting principles
Regulatory Assets [Line Items]
Cumulative effect reduction to retained earnings			53,880,000
Retained Earnings
Regulatory Assets [Line Items]
Cumulative effect reduction to retained earnings	(535,375,000)	$ (426,942,000)	(543,800,000)	$ (393,674,000)
Common stock repurchased	$ 1,489,000	$ 145,000
Retained Earnings | Cumulative effect of change in accounting principles
Regulatory Assets [Line Items]
Cumulative effect reduction to retained earnings			$ 53,880,000

Regulatory Matters - Actual Cap

Regulatory Matters - Actual Capital Amounts and Ratios (Details) $ in Thousands	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Consolidated
Total capital to risk weighted assets:
Actual Amount	$ 1,874,814	$ 1,825,661
Actual Ratio (percent)	0.1413	0.1332
Minimum for Capital Required - Basel III Amount	$ 1,393,602	$ 1,438,939
Minimum for Capital Required - Basel III Ratio (percent)	0.1050	0.1050
Tier 1 capital to risk weighted assets:
Tier One Risk Based Capital	$ 1,507,307	$ 1,471,841
Actual Ratio (percent)	0.1136	0.1074
Minimum for Capital Required - Basel III Amount	$ 1,128,154	$ 1,164,855
Minimum for Capital Required - Basel III (percent)	0.0850	0.0850
Common equity tier 1 to risk weighted assets:
Actual amount	$ 1,451,707	$ 1,416,241
Actual ratio (percent)	0.1094	0.1033
Minimum for Capital Required - Basel III Amount	$ 929,068	$ 959,293
Minimum for Capital Required - Basel III (percent)	0.0700	0.0700
Tier 1 capital to average assets:
Actual Amount	$ 1,507,307	$ 1,471,841
Actual Ratio (percent)	0.0901	0.0912
Minimum for Capital Required - Basel III Amount	$ 668,972	$ 645,730
Minimum for Capital Required - Basel III Ratio (percent)	0.0400	0.0400
Bank
Total capital to risk weighted assets:
Actual Amount	$ 1,904,255	$ 1,864,240
Actual Ratio (percent)	0.1435	0.1361
Minimum for Capital Required - Basel III Amount	$ 1,393,159	$ 1,438,385
Minimum for Capital Required - Basel III Ratio (percent)	0.1050	0.1050
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,326,819	$ 1,369,891
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	0.1000	0.1000
Tier 1 capital to risk weighted assets:
Tier One Risk Based Capital	$ 1,802,748	$ 1,776,420
Actual Ratio (percent)	0.1359	0.1297
Minimum for Capital Required - Basel III Amount	$ 1,127,796	$ 1,164,407
Minimum for Capital Required - Basel III (percent)	0.0850	0.0850
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,061,455	$ 1,095,913
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	0.0800	0.0800
Common equity tier 1 to risk weighted assets:
Actual amount	$ 1,802,748	$ 1,776,420
Actual ratio (percent)	0.1359	0.1297
Minimum for Capital Required - Basel III Amount	$ 928,773	$ 958,924
Minimum for Capital Required - Basel III (percent)	0.0700	0.0700
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 862,432	$ 890,429
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	0.0650	0.0650
Tier 1 capital to average assets:
Actual Amount	$ 1,802,748	$ 1,776,420
Actual Ratio (percent)	0.1078	0.1101
Minimum for Capital Required - Basel III Amount	$ 668,786	$ 645,539
Minimum for Capital Required - Basel III Ratio (percent)	0.0400	0.0400
To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 835,983	$ 806,924
To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (percent)	0.0500	0.0500

Subsequent Event (Details)

Subsequent Event (Details)	Apr. 22, 2021$ / shares
Subsequent Event
Subsequent Event [Line Items]
Dividends declared (usd per share)	$ 0.32